Fulvestrant plus palbociclib versus fulvestrant plus placebo for treatment of hormone-receptor-positive, HER2-negative metastatic breast cancer that progressed on previous endocrine therapy (PALOMA-3): final analysis of the multicentre, double-blind, phase 3 randomised controlled trial

Overall survival of palbociclib plus endocrine therapy in Japanese patients with HR+/HER2- advanced breast cancer in the first-or second-line setting: a multicenter observational study (P-BRIDGE study)

BACKGROUND

Recently, we reported the real-world effectiveness of palbociclib plus endocrine therapy (ET) in HR+/HER2- advanced breast cancer (ABC) in Japan (NCT05399329). However, median overall survival (OS) was not reached because of limited follow-up (36 months). Here, we present follow-up data from this study, including real-world clinical outcomes and treatment patterns.

METHODS

The P-BRIDGE study was a multi-center, observational study evaluating the real-world effectiveness and treatment patterns of patients diagnosed with HR+/HER2- ABC who received palbociclib plus ET in first (1L) or second line (2L) in Japan. The primary endpoint was real-world progression-free survival (rwPFS); secondary endpoints included OS and chemotherapy-free survival (CFS).

RESULTS

Of the 693 eligible patients, 426 and 267 patients received palbociclib with ET as 1L and 2L treatment, respectively. After a median follow-up of 48.1 months, the median rwPFS (95% CI) was 26.2 months (21.4-30.4) for 1L and 14.9 months (11.7-18.3) for 2L, respectively. Median OS (95% CI) was 68.2 months (60.8-NE) for 1L and 50.7 months (42.2-57.2) for 2L, respectively. OS analysis was also performed in the following subgroups: TFI < 12 months/TFI ≥ 12months/de novo metastatic median OS was 56.3 months (43.9-68.2), NR (NE-NE), NR (56.3-NE), visceral metastasis was 65.0 months (56.3-NE), liver metastasis was 46.4 months (37.2-NE), and bone only metastasis was NR (57.8-NE) in 1L, respectively.

CONCLUSIONS

The updated results from this study further confirm the real-world effectiveness of palbociclib plus ET in routine clinical practice in Japan. More than 5 years of median OS in 1L was observed, supporting the use of palbociclib plus ET as 1L standard of care for HR+/HER2- ABC.

Second-Line Endocrine Therapy With or Without Palbociclib Rechallenge in Patients With Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer: PALMIRA Trial

PURPOSE

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors plus endocrine therapy (ET) represents the standard first-line treatment for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HER2-negative) advanced breast cancer (ABC). However, there is no definitive consensus on the preferred second-line treatment option. The PALMIRA trial investigated whether palbociclib rechallenge with an alternative ET would improve the antitumor activity in patients progressing after a first-line palbociclib-containing regimen.

METHODS

This international, randomized, open-label, phase II study enrolled 198 patients with hormone receptor-positive/HER2-negative ABC with disease progression after first-line palbociclib plus ET (aromatase inhibitor or fulvestrant). Patients were eligible if they showed clinical benefit to the previous regimen (response or stable disease ≥24 weeks) or had progressed on a palbociclib-based therapy in the adjuvant setting. Patients were randomly assigned (2:1 ratio) to either palbociclib rechallenge plus second-line ET (fulvestrant or letrozole) or second-line ET alone. Stratification factors were previous ET and visceral involvement. The primary end point was investigator-assessed progression-free survival (PFS).

RESULTS

Between April 2019 and October 2022, 136 and 62 patients were randomly assigned to palbociclib plus ET or ET alone, respectively. Median investigator-assessed PFS was 4.9 months (95% CI, 3.6 to 6.1) with palbociclib plus ET versus 3.6 months (95% CI, 2.5 to 4.2) with ET alone (hazard ratio, 0.84 [95% CI, 0.66 to 1.07]; P = .149). Grade ≥3 treatment-emergent adverse events were higher with palbociclib plus ET (47.4% v 10.0%), without new safety signals.

CONCLUSION

Palbociclib rechallenge plus an alternative ET did not significantly improve PFS compared with ET alone in patients with hormone receptor-positive/HER2-negative ABC progressing on a first-line palbociclib-based ET regimen.

Baseline cell cycle and immune profiles indicate CDK4/6 inhibitor response in metastatic HR + /HER2- breast cancer

While CDK4/6 inhibitors (CDK4/6i) and endocrine therapy are standard-of-care for metastatic HR + /HER2- breast cancer, patient selection for durable efficacy remains undefined. Here, we assessed baseline cell cycle and immune profiles in a CDK4/6i-treated patient cohort with differential progression-free survival (PFS < 6 months vs. >23 months) using transcriptomic and protein-based imaging approaches. Cell cycle, polo-like kinase signaling and transcription gene sets are largely enriched among pre-treatment tissue of patients with short PFS. Pre-treatment tumors express cyclin A or E significantly higher in patients with short PFS and correlate with macrophage accumulation. Patients with long PFS display gene set enrichment for growth factor and immune signaling pre-treatment, while gene set enrichment for immune activation emerges during CDK4/6i therapy. Our data highlight baseline tumor-intrinsic and tumor microenvironments-associated indicators of CDK4/6i response in the "real-world" setting and offer implications for precision-based therapeutic combinations to enhance CDK4/6i efficacy. Clinical trial registration number: NCT04526587.

Development and Evaluation of a Remote Monitoring Regional Adjuvant Abemaciclib Service for Patients With High-Risk Early Breast Cancer

INTRODUCTION

Adjuvant abemaciclib was recently approved in high-risk early breast cancer, leading to an increase in oncology resource utilisation. We thus developed a regional, remote monitoring clinical service. The set-up, delivery processes and outcomes from the first 6 months' consecutive patients are presented.

METHODS

A regional delivery model with remote monitoring using optional electronic patient outcome measures (ePROMs) and bloods closer to home (BCTH) was implemented. Electronic patient records of patients entering the service (October 31, 2022 to May 31, 2023) were reviewed. Time-in-motion and on-line patient satisfaction surveys were conducted with questions adapted from prior questionnaires used by our cancer center. An independent t-test was used to assess differences in creatinine levels whilst on abemaciclib and a Mann-Whitney test to determine whether the time taken to complete follow-up appointments differed with and without ePROMs.

RESULTS

The first 103 patients to commence abemaciclib (median age 58 [range, 27-85], 66.0% White) had completed a median of 6 cycles (range, 0-9). 51.5% had treatment interruption, 52.4% a dose reduction and 15.5% discontinued therapy. Diarrhoea (90.3%), fatigue (84.9%) and anorexia (73.1%) were the most commonly reported toxicities on ePROMs. 10.8% of patients reported grade 3-4 toxicities. Neutropenia was also common and low grade. 89.5% of patients would recommend ePROMs and 98.0% found the BCTH service easy to use. Review appointments with ePROMs were a similar length to those without (P = .138).

CONCLUSIONS

We have successfully implemented a remote, regional adjuvant clinical service which could serve as a blueprint for other NHS trusts for this and other cancer drugs.

Raddeanin A exerts potent efficacy against non-small cell lung cancer by inhibiting cyclin-dependent kinase 6

PURPOSE

The aim of this study was to investigate the anti-tumor effects and mechanisms of Raddeanin A in NSCLC in vitro and in vivo.

METHODS

The effects of Raddeanin A on cell cycle progression, proliferation, migration and invasion of NSCLC were assessed by flow cytometry and cell biological assays in multiple NSCLC cell lines. To identify possible targets of Raddeanin A in NSCLC, we employed a multifaceted approach incorporating network pharmacology, molecular docking, and molecular dynamics simulation, along with additional techniques such as SPR (Surface Plasmon Resonance), Co-IP (Co-Immunoprecipitation), and immunofluorescence. In vivo effects were investigated using a nude mouse xenograft tumor model.

RESULTS

Raddeanin A inhibits NSCLC cell survival, inhibits invasion and migration and causes cell cycle arrest in G1 phase. Raddeanin A impacts NSCLC cellular activity by inhibiting CDK6, leading to anti-tumor effects. Molecular analysis confirms that the tight binding between Raddeanin A and CDK6, facilitated by specific hydrogen bonds at binding sites including VAL-101, HIS-100, GLN-149, LYS-147, THR-182, VAL-180, and ALA-23, stabilizes within the 40-100 ns interval. In a nude mouse xenograft tumor model, Raddeanin A also demonstrated an inhibitory effect on NSCLC tumor growth.

CONCLUSIONS

Raddeanin A blocks the cell cycle in G1 phase by inhibiting CDK6. Raddeanin A is expected to be a novel antitumor agent against NSCLC.

Incidence of Metastasis in the Central Nervous System in Advanced Breast Cancer Treated With CDK 4/6 Inhibitors: A Multicenter, Retrospective Study

Central nervous system (CNS) metastasis remains a major cause of mortality in advanced breast cancer (ABC). While cyclin-dependent kinase 4/6 inhibitors (CDKIs) combined with endocrine therapy (ET) delay resistance in hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative ABC, their impact on CNS metastasis development has not been fully elucidated. This retrospective study analyzed 435 ABC patients without baseline CNS metastases who received first-line ET with or without CDKIs across three Chinese hospitals (August 2018-July 2022). Primary end points included CNS as the first metastatic site, CNS metastasis-free survival (CNSM-FS), and CNS metastasis incidence over time. Secondary end points were progression-free survival (PFS) and overall survival (OS). The results indicated that the addition of CDKIs to ET significantly reduced the incidence of CNS as the first site of metastasis (3.7% vs. 9.5% with ET alone; p = 0.0015) and extended CNSM-FS (71.6 months vs. 63.6 months, respectively; hazard ratio [HR], 0.53; 95% CI, 0.31-0.92). Overall, CNS metastasis incidence was lower with ET + CDKIs (7.9% vs. 15.5%, p = 0.014), and improvements were observed in both PFS and OS. These findings suggest that ET + CDKIs as first-line therapy in ABC may reduce CNS metastasis risk and extend CNSM-FS, offering a potential strategy for preventing CNS metastases.

Zanidatamab plus palbociclib and fulvestrant in previously treated patients with hormone receptor-positive, HER2-positive metastatic breast cancer: primary results from a two-part, multicentre, single-arm, phase 2a study

BACKGROUND

New HER2-targeted regimens, including chemotherapy-free options, are needed for metastatic breast cancer. In an ongoing, two-part, phase 2a study, we assessed the safety and antitumour activity of zanidatamab, a HER2-targeted bispecific antibody, plus palbociclib and fulvestrant, in heavily pretreated patients with hormone receptor-positive, HER2-positive advanced or metastatic breast cancer.

METHODS

This multicentre, single-arm, two-part, phase 2a study is being conducted at 13 university hospitals, cancer centres, or research institutes in Spain, Canada, and the USA. Eligible patients were adults (aged ≥18 years) with an Eastern Cooperative Oncology Group performance status of 0 or 1, and with pathologically confirmed unresectable or metastatic breast cancer, assessed locally to be hormone receptor-positive and HER2-positive, with disease progression during or after previous HER2-targeted therapies. Patients were enrolled in part 1, part 2, or part 1 followed by part 2. In part 1, patients received starting doses of zanidatamab (20 mg/kg intravenously once every 2 weeks on days 1 and 15 of a 28-day cycle) with palbociclib (125 mg orally once a day on days 1-21 of each cycle) and fulvestrant (500 mg intramuscular injection once every 2 weeks for the first three doses [cycle 1: days 1 and 15, cycle 2: day 1], then once every 4 weeks [all subsequent cycles: day 1]). In part 1, primary endpoints were safety of the triplet combination and confirmation of recommended doses for part 2. In part 2, patients received the recommended doses confirmed in part 1, and the primary endpoint was progression-free survival at 6 months. Safety and progression-free survival were assessed in all enrolled patients who received any dose of zanidatamab, palbociclib, or fulvestrant. Patients in part 1 who were treated at the recommended doses were analysed together with the patients in part 2. This study is registered with ClinicalTrials.gov, NCT04224272, and is active with recruitment completed.

FINDINGS

Overall, 51 patients (49 [96%] female and two [4%] male; median age 54·0 [46·0-62·0] years; 42 [82%] White) were enrolled: eight in part 1 (June 10, 2020-Feb 7, 2021) and 43 in part 2 (Feb 8, 2021-Oct 31, 2022). All 51 patients had received study treatment at the data cutoff (Aug 3, 2023); median follow-up was 16·1 months (IQR 9·9-23·4) and the median duration of triplet regimen treatment was 7·4 months (3·4-14·8). The median number of previous HER2-targeted therapies was 4 (IQR 3-4). 12 (24%) of 51 patients had previously received trastuzumab deruxtecan. The planned starting drug doses administered in part 1 of the study were confirmed as the recommended doses for part 2. All 51 patients were treated at the recommended doses. All 51 patients had at least one treatment-related adverse event of any grade, with diarrhoea being the most common (41 [80%] patients, with 34 [67%] having grade 1-2 events). Grade 3 or 4 treatment-related adverse events occurred in 34 (67%) patients, with neutropenia being the most common (26 [51%] patients). One (2%) patient had a serious grade 3 treatment-related adverse event of increased transaminases. No treatment-related deaths occurred. In the overall sample (N=51), progression-free survival at 6 months was 66·7% (95% CI 52·1-79·2).

INTERPRETATION

Zanidatamab plus palbociclib and fulvestrant was generally safe and showed promising antitumour activity, supporting further evaluation of this chemotherapy-free triplet regimen.

FUNDING

Zymeworks, Jazz Pharmaceuticals, and Pfizer.

Management of Metastatic Hormone Receptor-Positive Breast Cancer Beyond CDK4/6 Inhibitors

PURPOSE OF REVIEW

Since the introduction of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) as the first-line treatment for metastatic hormone receptor (HR) positive, human epidermal growth factor receptor 2 (HER2) negative (HR+/HER2-) breast cancer, there has been a significant expansion in the number of therapeutic options for subsequent lines of therapy. Many new agents are being studied, with potential for future regulatory approval. The increased number of therapeutic options raises questions about the optimal selection and sequencing of therapies for individual patients. These advances represent an important clinical challenge in this rapidly evolving field, given the introduction of new therapies targeting various pathways (alone or in combination) and new therapeutic classes being studied.

RECENT FINDINGS

Recently approved targeted therapies have demonstrated improvements in progression free survival (PFS) for patients whose cancer harbors mutations in the PI3K/AKT pathway, ESR1, BRCA1/2, and/or PALB2. Data to support continuation of CDK4/6 inhibition after progression on a prior CDK4/6i remains mixed, though some studies suggest a subset of patients may benefit from this approach. Several agents with unique mechanisms of action have shown promise in data from early phase trials, and have the potential to enter the treatment lexicon in the coming years. Examples include CDK2- and CDK4-selective inhibitors, complete estrogen receptor antagonists (CERANs), proteolysis targeting chimeras (PROTACs), and next-generation PI3K pathway inhibitors. In this narrative review, we summarize the current and upcoming treatments for metastatic HR+/HER2- breast cancer after progression on a CDK4/6i plus ET, with a focus on the following: an overview of first-line regimens of CDK4/6i plus ET and observed mechanisms of resistance; currently approved second-line therapy options; and upcoming options currently under exploration in clinical trials. We focus primarily on new therapy classes that may offer therapeutic options beyond currently available treatments.

A phase I dose-escalation and dose-expansion study of tibremciclib, a novel CDK4/6 inhibitor, monotherapy and in combination with fulvestrant in HR-positive/HER2-negative advanced breast cancer

BACKGROUND

Tibremciclib (BPI-16350) is a novel potent selective inhibitor of cyclin-dependent kinase 4 and 6 (CDK4/6). This phase I, first-in-human study assessed the tibremciclib monotherapy and combined with fulvestrant in advanced breast cancer (ABC).

PATIENTS AND METHODS

This open-label, phase I study (NCT03791112) comprised dose escalation (phase Ia) and expansion (phase Ib). In phase Ia, Chinese patients with advanced solid tumors received tibremciclib monotherapy (50-500 mg orally once daily). Based on the tolerability and preliminary antitumor activity from phase Ia, two dose cohorts (300 or 400 mg orally once daily) were selected in phase Ib to combine with fulvestrant in patients with hormone receptor (HR)-positive/human epidermal growth receptor 2 (HER2)-negative ABC who failed endocrine therapy. The primary endpoints were safety and tolerability, and secondary endpoints included pharmacokinetics (PK) and antitumor activity.

RESULTS

In phase Ia, 24 patients with advanced tumors (23 ABC and 1 abdominal liposarcoma) received tibremciclib monotherapy, while in phase Ib, 78 patients with HR-positive/HER2-negative stage IV ABC received tibremciclib plus fulvestrant, with a median age of 56.0 (range 26-66) years and 53.5 (range 33-71) years, respectively. In phase Ia, one dose-limiting toxicity (grade 3 blood creatinine increased) occurred at 500 mg and the maximum tolerated dose was not reached. In phase Ib, the recommended phase II dose (RP2D) was tibremciclib 400 mg plus fulvestrant 500 mg. Frequently reported treatment-emergent adverse events of any grade were grade 1-2 blood creatinine increased, hypertriglyceridemia, and anemia. PK demonstrates dose proportionality, a half-life of ∼35.9-51.1 h, and no drug-drug interaction with fulvestrant. In phase Ia, one patient achieved partial response (PR), with a confirmed objective response rate (ORR) of 4.2% and a disease control rate (DCR) of 70.8%. In phase Ib, 42 patients achieved PR, with an ORR of 53.8% and a DCR of 87.2%.

CONCLUSIONS

Tibremciclib monotherapy or combined with fulvestrant was well tolerated with the RP2D set at 400 mg plus fulvestrant 500 mg. PK was consistent with dose proportionality. Both regimens showed preliminary antitumor activity in patients with HR-positive/HER2-negative ABC, supporting further evaluation in a phase III study (NCT05433480).

CDK4/6 inhibitors in breast cancer therapy: mechanisms of drug resistance and strategies for treatment

Dysregulated cell cycle progression is a well-established hallmark of cancer, driving the development of targeted antitumor therapies that intervene at specific phases of the cell cycle. Among these therapeutic targets, cyclin-dependent kinases 4 and 6 (CDK4/6) have emerged as critical regulators of cell cycle progression, with their aberrant activation being strongly implicated in tumorigenesis and cancer progression. Currently, multiple CDK4/6 inhibitors have received clinical approval for hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative breast cancer, demonstrating dual therapeutic mechanisms through both cell cycle arrest and enhancement of antitumor immunity. However, clinical implementation faces two major challenges: the inevitable development of acquired resistance during prolonged treatment, and the need for optimized combination strategies with other anticancer agents to achieve synergistic efficacy. This review systematically examines the molecular mechanisms underlying CDK4/6 inhibitor function and characterizes currently approved therapeutic agents. Importantly, it synthesizes recent discoveries regarding resistance mechanisms, including dysregulated cell cycle checkpoints, compensatory signaling pathway activation, and tumor microenvironment adaptations. Furthermore, we critically evaluate emerging combination therapeutic approaches targeting these resistance mechanisms. By integrating mechanistic insights with clinical evidence, this analysis aims to provide actionable strategies for overcoming therapeutic resistance and maximizing the clinical potential of CDK4/6 inhibitors in breast cancer management.

Targeting autophagy plus high-dose CDK4/6 inhibitors in advanced HR+HER2- breast cancer: A phase 1b/2 trial

BACKGROUND

The unmet needs of managing patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) breast cancer who progress after cyclin-dependent kinase (CDK)4/6 inhibitor (CDK4/6i) treatment remain unclarified.

METHODS

This was a phase 1b/2, single-arm, open-label study that enrolled 29 patients with HR+/HER2- breast cancer who experienced first-line palbociclib treatment failure. The primary endpoint was the incidence of dose-limiting toxicity (DLT). The secondary endpoints were the objective response rate (ORR) and progression-free survival (PFS). The clinical trial registration number is ClinicalTrials.gov: NCT05953350.

FINDINGS

The phase 1b study demonstrated no DLT in patients treated with hydroxychloroquine (HCQ; 600 mg, bis in die [bid]) plus increasing doses of palbociclib (100, 150, or 200 mg, quaque die [qd]). The plasma pharmacokinetics of palbociclib were not significantly affected by HCQ. The recommended phase 2 dose (RP2D) was HCQ (600 mg, bid) plus palbociclib (200 mg, qd). The dose-expansion cohort demonstrated that HCQ plus palbociclib (200 mg, qd) treatment was tolerable. Grade 3 treatment-emergent adverse events (TEAEs) with an incidence higher than 15.0% included neutropenia (25.0%), leukopenia (25.0%), fatigue (20.0%), and back pain (15.0%). The ORR of all enrolled patients in our present trial was 41.4% (12/29). In the dose-expansion cohort, with the last enrolled patient having a follow-up duration of 32.3 weeks, the median PFS was not reached. The clinical benefit rate (CBR) at 6 months was 90.0% (95% confidence interval [CI]: 68.3%-98.8%). These findings were supported by preclinical data.

CONCLUSIONS

Combined HCQ with high-dose CDK4/6i palbociclib (200 mg, qd) showed tolerable toxicity and promising efficacy for patients with advanced HR+/HER2- breast cancer after CDK4/6i failure.

FUNDING

This work was funded by the National Natural Science Foundation of China.

Combination therapy and dual-target inhibitors based on cyclin-dependent kinases (CDKs): Emerging strategies for cancer therapy

Cyclin-dependent kinases (CDKs) are pivotal regulators of the cell cycle and transcriptional machinery, making them attractive targets for cancer therapy. While CDK inhibitors have demonstrated promising clinical outcomes, they also face challenges in enhancing efficacy, particularly in overcoming drug resistance. Combination therapies have emerged as a key strategy to augment the effectiveness of CDK inhibitors when used alongside other kinase inhibitors or non-kinase-targeted agents. Dual-target inhibitors that simultaneously inhibit CDKs and other oncogenic drivers are gaining attention, offering novel avenues to optimize cancer therapy. Based on the structural characterization and biological functions of CDKs, this review comprehensively examines the structure-activity relationship (SAR) of existing dual-target CDK inhibitors from a drug design perspective. We also thoroughly investigate the preclinical studies and clinical translational potential of combination therapies and dual-target inhibitors. Tailoring CDK inhibitors to specific cancer subtypes and therapeutic settings will inspire innovative approaches for the next generation of CDK-related therapies, ultimately improving patient survival.

Optimization of carbon membrane performance in reverse osmosis systems for reducing salinity, nitrates, phosphates, and ammonia in aquaculture wastewater

This study investigates the performance of various types of carbon membranes in reverse osmosis systems aimed at reducing salinity, nitrates, phosphates, and ammonia in aquaculture wastewater. As sustainable aquaculture practices become increasingly essential, effective treatment solutions are needed to mitigate pollution from nutrient-rich effluents. The research highlights several carbon membranes types, including carbon molecular sieves, activated carbon membranes, carbon nanotube membranes, and graphene oxide membranes, all of which demonstrate exceptional filtration capabilities due to their unique structural properties. Findings reveal that these carbon membranes can achieve removal efficiencies exceeding 90 % for critical pollutants, thereby significantly improving water quality and supporting environmental sustainability. The study also explores the development of hybrid membranes and nanocomposites, which enhance performance by combining the strengths of different materials, allowing for customized solutions tailored to the specific requirements of aquaculture wastewater treatment. Additionally, operational parameters such as pH, temperature, and feed water characteristics are crucial for maximizing membrane efficiency. The integration of real-time monitoring technologies is proposed to enable prompt adjustments to treatment processes, thereby improving system performance and reliability. Overall, this research emphasizes the importance of interdisciplinary collaboration among researchers and industry stakeholders to drive innovation in advanced filtration technologies. The findings underscore the substantial potential of carbon membranes in tackling the pressing water quality challenges faced by the aquaculture sector, ultimately contributing to the sustainability of aquatic ecosystems and ensuring compliance with environmental standards for future generations.

Cyclin-dependent kinase 4 and 6 inhibitors in breast cancer treatment

Breast cancer is the second largest cancer in the world, and it has highest mortality rate in women worldwide. The aberrant activation of the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway plays an important role in uncontrolled breast cancer cell proliferation. Therefore, targeting CDK4/6 to improve overall survival rates has been a strong interest in breast cancer therapeutics. Till date, four CDK4/6 inhibitors have been developed and approved for hormone receptor-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer therapies with great success. However, acquired resistance to CDK4/6 inhibitors has emerged and limits their effectiveness in breast cancer. In this review, we systematically discussed the mechanisms of resistance to CDK4/6 inhibitors including the cell cycle-specific and cell cycle-nonspecific mechanisms. Also, we analyzed combination strategies with other signaling inhibitors in clinical and preclinical settings that further expand the clinical application of CDK4/6 inhibitors in future breast cancer therapies.

Using prognostic signatures and machine learning to identify core features associated with response to CDK4/6 inhibitor-based therapy in metastatic breast cancer

CDK4/6 inhibitors in combination with endocrine therapy are widely used to treat HR+/HER2- metastatic breast cancer leading to improved progression-free survival (PFS) compared to single agent endocrine therapy. Over 300 patients receiving standard-of-care CDK4/6 inhibitor combination therapy for metastatic disease were enrolled at a single institution. Clinical, pathological, and gene expression data were employed to define determinants for PFS duration. Visceral disease (HR 1.55, p = 0.0013), prior endocrine therapy (HR 2.34, p < 0.001), and the type of endocrine therapy (HR 2.16, p < 0.001) were highly associated with PFS duration. Multiple pre-defined gene expression signatures were employed to determine association with response to CDK4/6 inhibitor-based therapy. Random survival forest was applied to define key gene expression and clinical features associated with PFS and develop a predictive model. The time to progression predicted by this model was related to the median PFS observed in PALOMA-2/3 and PEARL studies. Interrogating genes identified as highly significant across all studies indicated common enrichment of gene networks associated with cell cycle and estrogen receptor signaling. These findings indicate that there are common features from real-world use of CDK4/6 inhibitors that could be used to infer time to progression and better inform treatment.

CDK4/6 inhibition in early and advanced hormone receptor-positive, HER2-negative breast cancer

INTRODUCTION

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibition in combination with endocrine therapy is the mainstay of treatment for hormone receptor-positive, HER2-negative (HR  +  /HER2-) advanced breast cancer; the CDK4/6 inhibitors abemaciclib and ribociclib are also approved for high-risk, early-stage, HR  +  /HER2- breast cancer. Numerous studies exploring CDK4/6 inhibitors in the early-stage setting are ongoing, as well as many more exploring novel combinations in the metastatic setting.

AREAS COVERED

Here, we review the basis of CDK4/6 inhibition for HR  +/HER2- breast cancer, the pivotal clinical trials which led to regulatory approval, and ongoing trials evaluating novel combinations to further improve outcomes for those with both early and advanced HR+/HER2- breast cancer. Current literature was reviewed by a comprehensive search of PubMed MEDLINE (1/1/2000-12/31/2024).

EXPERT OPINION

CDK4/6 inhibitors are integral in the management of both advanced and high-risk, early-stage HR  +  /HER2- breast cancer. Biomarkers predictive of CDK 4/6 inhibitor (CDK4/6i) benefit remain elusive, and clinical and pathological features remain key to identifying those who are candidates for CDK4/6 inhibition in the early-stage setting. Numerous trials evaluating the role of a CDK4/6i with novel endocrine therapy partners and other targeted agents are ongoing, with the goal of improving outcomes for those with HR  +  /HER2- disease.

Treatment Sequencing in Metastatic HR+/HER2- Breast Cancer: A Delphi Consensus

Background: The treatment landscape in HR+/HER2- metastatic breast cancer (mBC) is continuously evolving, with evidence on new agents and combinations published almost every year. Despite updated therapeutic guidelines, second-line (2L) selection may be challenging due to clinical factors, biomarker status, and available agents. Methods: A two-round Delphi consensus was organized in July 2024, gathering input from 10 experts in research, diagnosis, and treatment of HR+/HER2- mBC on optimal 2L and beyond choice, considering the available biomarkers and results from published clinical trials. Consensus was defined as 70% agreement or disagreement. Results: The experts considered initially a list of 39 statements, structured into the following four sections: biomarker testing; selection of 2L treatment at progression of disease on first line endocrine therapy (ET) + CDK4/6i at ≥6 months after initiation of ET for mBC; selection of 2L treatment at disease progression on ET + CDK4/6i, at <6 months after initiation of ET for mBC, whilst on ET; and selection of post-2L treatment options. After a discussion, the experts decided to remove four statements, refine ten, and include three new ones. The final list consisted of 38 statements, and consensus was achieved in 37. Conclusions: The panel recommends next-generation sequencing as the method of choice for genomic characterization at disease progression on first line. The optimal agent or treatment class is indicated depending on the presence of specific mutations; however, the panel admits that the strategy is different in clinical practice, where novel therapies might not be available or reimbursed.

Cost-effectiveness of CDK4/6 inhibitors for second-line HR+/HER2- advanced or metastatic breast cancer in China

Hormone receptor HR-positive/HER2-negative (HR+/HER2-) breast cancer is the most common subtype in China, representing 60-70% of cases, with a rising incidence due to aging demographics and lifestyle changes. CDK4/6 inhibitors such as palbociclib, ribociclib and abemaciclib have been proven effective in treating HR+/HER2 - advanced or metastatic breast cancer (ABC/MBC), though they may increase healthcare costs. This study aims to compare the efficacy, safety and cost-effectiveness of CDK4/6 inhibitors for the second-line treatment of HR+/HER2 - ABC/MBC from the Chinese healthcare perspective. A cohort-based partitioned survival model was utilized, drawing on the survival data published from PALOMA-3, MONALEESA-3 and MONARCH-2 trials. Costs, and quality-adjusted life years (QALYs) were used to calculate the incremental cost-effectiveness ratio (ICER) over a 15-year time horizon. Deterministic and probabilistic sensitivity analyses were performed to assess the robustness of the model results. In the base-case analysis, the model estimated health benefits to be 2.10 QALYs for palbociclib plus fulvestrant (PAL + FUL), 2.55 QALYs for ribociclib plus fulvestrant (RIB + FUL), and 2.60 QALYs for abemaciclib plus fulvestrant (ABE + FUL), with corresponding costs of $34,423, $41,119, and $48,019. Compared with PAL + FUL, the ICERs were $27,161 per QALY for ABE + FUL and $15,073 per QALY for RIB + FUL. The robustness of these findings was confirmed through uncertainty analyses. Among the three strategies, the most cost-effective probabilities of PAL + FUL, RIB + FUL and ABE + FUL were 0%, 99.8%, and 0.2% under the willingness-to-pay (WTP) threshold of 3 times per-capita gross domestic product ($37,738) in China. This study indicated that both RIB + FUL and ABE + FUL are cost-effective at the WTP threshold compared with PAL + FUL. Notably, RIB + FUL offers the greatest cost-effective advantage for the second-line treatment of HR+/HER2 - ABC/MBC among these three CDK4/6 inhibitors.

Metronomic Capecitabine Plus Aromatase Inhibitor as Initial Therapy in Patients With Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer: The Phase III MECCA Trial

PURPOSE

The effects of metronomic chemotherapy plus endocrine therapy have yet to be elucidated through a randomized phase III clinical trial.

METHODS

Randomized clinical trials were conducted at 12 centers in China from August 22, 2017, to September 24, 2021, and the final follow-up date was August 25, 2023. Patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC) who had no previous systemic therapy in the metastatic setting were enrolled. Participants were 1:1 assigned to receive either metronomic capecitabine plus an aromatase inhibitor (AI) or AI alone. The primary end point was progression-free survival (PFS). Secondary end points included overall survival (OS), objective response rate, disease control rate (defined as disease controlled for ≥24 weeks), and safety.

RESULTS

A total of 263 patients were randomly assigned, among which 254 patients formed the full analysis set. At the median follow-up time of 50.7 months, 203 PFS events occurred. The metronomic capecitabine plus AI arm exhibited a median PFS of 20.9 months compared with 11.9 months in the AI arm (hazard ratio [HR], 0.58 [95% CI, 0.43 to 0.76]). The median OS was not reached in the combination arm and was 45.1 months in the AI arm (HR, 0.58 [95% CI, 0.37 to 0.93]). The most common adverse events were palmar-plantar erythrodysesthesia and peripheral neuropathy; grade 3 events occurred in 15.1% of the patients receiving combination treatment.

CONCLUSION

The MECCA trial demonstrated a significant improvement in PFS and OS with first-line metronomic capecitabine plus AI compared with AI alone in patients with hormone receptor-positive+/HER2-negative MBC. Both treatment arms exhibited tolerable safety profiles consistent with previous reports.

General Anesthesia Surgery for Early Breast Cancer in a Patient with Severe Heart Failure due to Dilated Cardiomyopathy: A Case Report

INTRODUCTION

Perioperative mortality is significantly higher in cases of heart failure with severe left ventricular ejection fraction (LVEF) reduction, making it challenging to decide whether to proceed with surgery for early-stage breast cancer, which is not immediately fatal. However, the prognosis of heart failure has improved and breast cancer is increasingly becoming a prognostic factor. Herein, we report the case of a breast cancer patient with severe heart failure due to dilated cardiomyopathy (DC), who was deemed fit to undergo surgery under general anesthesia after obtaining sufficient informed consent and achieving improvement in heart failure symptoms during endocrine therapy.

CASE PRESENTATION

A 64-year-old female with a history of DC and sustained ventricular tachycardia, who had received cardiac resynchronization therapy with defibrillator implantation, underwent breast cancer surgery. She had been repeatedly hospitalized for heart failure with an LVEF of 19% and New York Heart Association (NYHA) Class III status, and heart transplant surgery was considered. However, a screening computed tomography scan revealed right breast cancer, and neither heart transplantation nor breast cancer surgery was performed. Endocrine therapy was initiated and failed 48 months after administration. Although the LVEF remained low at 21%, the NYHA classification improved to Class II, and she had not been hospitalized for heart failure for an extended period since her breast cancer diagnosis. Therefore, breast cancer surgery was performed under general anesthesia and no postoperative complications were observed throughout the course of the surgery.

CONCLUSION

Given that the prognosis for heart failure may statistically be better than that for breast cancer, early breast cancer surgery should be performed in patients with stable heart failure symptoms.

Bireociclib plus fulvestrant for HR+/HER2- advanced female breast cancer progressed on or after endocrine therapy: phase 3 BRIGHT-2 study interim analysis

The BRIGHT-2 study (NCT05077449) is a randomized, double-blind, placebo-controlled, phase 3 trial evaluating the efficacy and safety of bireociclib plus fulvestrant (BF) vs. placebo plus fulvestrant (F) in Chinese female patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) advanced breast cancer (ABC) who had progressed on or after prior endocrine therapy (ET). Interim results were analyzed after 70% of progression-free survival (PFS) events across 64 centers in China between December 8, 2021, and March 28, 2023. Patients were randomized (2:1) to receive BF or F, with stratification based on visceral involvement (yes/no) and resistance to prior primary or secondary ET. As the primary outcome, PFS was significantly prolonged in the BF group (n = 204) (12.94 months; 95% CI: 11.07-not reached) compared to 7.29 months (95% CI: 5.45-11.04) in the F group (n = 101) (hazard ratio, 0.56; 95% CI: 0.39-0.80; p = 0.001). The objective response rate in the BF group was 39.7% in the intention-to-treat population. Grade ≥3 adverse events were more frequent in the BF group (64.7%) than in the F group (18.8%), with neutropenia, leukopenia, and anemia being the most common. These findings suggest that BF is a promising therapeutic option for patients with HR+/HER2- ABC following ET failure.

Detection of ESR1 Mutations in Tissue and Liquid Biopsy with Novel Next-Generation Sequencing and Digital Droplet PCR Assays: Insights from Multi-Center Real Life Data of Almost 6000 Patients

BACKGROUND

ESR1 mutations are biomarkers in breast cancer patients who develop metastatic disease after endocrine therapy (ET). Recently, the Food and Drug Administration (FDA) and European Medicines Agency (EMA) have approved Elacestrant, a selective estrogen receptor degrader for patients harboring ESR1 mutations. This has necessitated the establishment of reliable and sensitive NGS- or PCR-based assays to detect these ESR1 resistance mutations in liquid biopsy samples.

METHODS

We evaluated NGS results of a pan-cancer cohort of almost 6000 patients from two major German institutes of pathology, to show that the occurrence of ESR1 mutations is extremely rare (<1%) in ET-naïve patients. This suggests that ESR1 mutations arise almost exclusively under the pressure of ET. Therefore, we designed a breast cancer-specific hybrid capture-based NGS liquid biopsy assay covering 12 breast cancer-related genes, including ESR1, PIK3CA, AKT1, ERBB2, BRCA1/2, and TP53. We validated the HS2-Mamma-LIQ assay extensively using reference material to detect mutations to 0.1% variant allele frequency (VAF) and compared the performance to a commercially available ESR1 ddPCR assay.

RESULTS

We show the results of routine diagnostic analysis of the first consecutive 354 patients with activating ESR1 mutations rate of 43%, with 20% of patients harboring co-mutations in PIK3CA and other genes underlining the relevance of tumor heterogeneity. Our study highlights liquid biopsy as a preferred approach for monitoring ESR1 mutations in breast cancer patients by showing cases where NGS analysis suggests complex tumor heterogeneity with multiple ESR1 as well as PIK3CA mutations at different VAFs.

CONCLUSIONS

Our findings not only corroborate prior research concerning the rarity of these mutations in unselected patients but also emphasize the importance of robust and broad molecular assays rather than single gene assays in their detection and characterization in the diagnostic setting. Advantages of different approaches are discussed to address the current clinical need.

Novel strategies in breast cancer management: From treatment to long-term remission

Breast cancer (BC) is the most common malignancy among women and a leading cause of cancer-related mortality worldwide. Although improvements in early detection and therapy have been made, metastatic breast cancer (mBC) continues to be an incurable disease. Although existing treatments can prolong survival and enhance quality of life, they do not provide a definitive cure. Targeted therapies have significantly improved outcomes, particularly for subtypes such as human epidermal growth factor receptor 2 (HER2)-positive and hormone receptor (HR)-positive (HR+) BC. Key innovations include antibodydrug conjugates (ADCs) and next-generation endocrine therapies. ADCs combine monoclonal antibodies with cytotoxic agents, allowing targeted delivery to tumor cells while minimizing systemic toxicity. Immunotherapy is emerging as a promising approach for aggressive subtypes, such as triple-negative breast cancer (TNBC). Strategies under investigation include chimeric antigen receptor T-cell (CAR-T) therapy, tumor-infiltrating lymphocyte (TIL) therapies, and natural killer (NK) cell treatments, all aimed at enhancing the ability of the immune system to target and eliminate resistant tumor cells. Tissue engineering, particularly hydrogel-based delivery systems, offers the potential for localized treatment. These systems enable the controlled release of therapeutic agents or immune cells directly to the tumor site, supporting tissue regeneration and enhancing immune surveillance to reduce recurrence. Despite these advancements, challenges remain, including treatment resistance, the immunosuppressive tumor microenvironment, and high costs. Overcoming these barriers requires further innovation in drug delivery systems and a deeper understanding of tumor biology.

Novel Estrogen Receptor - Targeted Therapies in Hormone-Receptor Positive Breast Cancer

OPINION STATEMENT

Endocrine therapy is the backbone of treatment for HR + /HER2- MBC. The introduction of novel endocrine-based therapies has changed the landscape of metastatic breast cancer care, with even more promising agents on the horizon. Given the consistent success in prolonging PFS and OS, CDK4/6 inhibitors should be used as first-line treatment. Once secondary resistance eventually develops after use of a CDK4/6 inhibitor, use of monotherapy with either AI or fulvestrant has shown poor outcome. For example, in the control group of the EMERALD trial, in which all the patients were required to have previously received a CDK4/6 inhibitor, median progression-free survival with endocrine therapy was only 1.9 months. Based on the emerging evidence, molecular profiling of tissue or liquid biopsy at progression of disease is crucial to select future therapy. For patients whose tumors harbor ESR1 mutations, oral SERDs are the preferred option. For those with PIK3CA or AKT1 mutation or PTEN inactivation, combination therapy with the AKT pathway inhibitor capivasertib is recommended. Alpelisib, the first AKT1 inhibitor approved in combination therapy with fulvestrant in PIK3CA mutated tumors only, is now less in favor given its challenging side effect profile. When mutations are not present, options include combination therapy with the mTOR inhibitor everolimus or changing endocrine therapy and continuing a CDK 4/6 inhibitor. In patients with short response to CDK4/6 inhibitors suggesting endocrine resistant disease, chemotherapy or antibody-drug conjugates should be considered. With better understanding of the mechanisms of resistance to CDK4/6 inhibitors, additional mutations could be identified and potentially targeted in order to provide individualized treatment options. Optimal sequencing of treatment options depends on several factors: (1) the presence of specific molecular aberrations; (2) previous treatment history, duration of response and patient's performance status; (3) balance between maximizing survival benefits with quality of life/toxicities; (4) disease burden. In the upcoming years, we anticipate FDA approvals for more of the SERD molecules both in monotherapy and in combination therapy which will continue to expand the options available for HR + /HER2- MBC patients.

Effect of palbociclib plus letrozole on patient-reported health-related quality of life: extended follow-up of the PALOMA-2 trial

BACKGROUND

Metastatic breast cancer (mBC) remains incurable, highlighting the importance of patient-reported outcomes (PROs) in treatment decision making. In the randomized phase III PALOMA-2 trial, health-related quality of life (HRQoL) was maintained in patients receiving first-line palbociclib plus letrozole compared with placebo plus letrozole after a median follow-up of 22.3 months. However, little is known about HRQoL for patients taking palbociclib for an extended period of time. Here, we report the PRO results from the PALOMA-2 trial after a median follow-up time of 90 months.

PATIENTS AND METHODS

Women with estrogen receptor-positive/human epidermal growth factor receptor 2-negative (ER+/HER2-) mBC were randomly assigned 2 : 1 to receive palbociclib plus letrozole (n = 444) or placebo plus letrozole (n = 222). HRQoL was assessed with the Functional Assessment of Cancer Therapy-Breast (FACT-B) and EuroQoL five-dimensions three-level (EQ-5D-3L) questionnaires, administered on site on day 1 of cycles 1, 2, and 3 and then every other cycle from cycle 5 until study end. Treatment arm comparisons were made for change from baseline in QoL and time to deterioration in FACT-B (definitive definition, TTDD).

RESULTS

After a median follow-up of 90 months, no significant differences between treatments were observed for overall change from baseline in FACT-B total, FACT-B subscales, and EQ-5D-3L scores. While TTDD did not differ between treatment arms, TTDD was shorter for patients with disease progression versus those without disease progression (hazard ratio 0.644, P < 0.001). Individual items assessing side-effects and hair loss favored the palbociclib plus letrozole arm versus the letrozole arm; no treatment difference was observed for items assessing pain.

CONCLUSIONS

This extended follow-up analysis of PROs in PALOMA-2 shows continued QoL maintenance for patients with ER+/HER2- mBC receiving long-term palbociclib plus letrozole treatment.

Pseudo acute kidney injury in patients receiving CDK4/6 inhibitors

INTRODUCTION

CDK4/6 inhibitors (CDK4/6i) improve progression-free survival in patients with advanced oestrogen-receptor-positive breast cancer. However, all CDK4/6i may increase creatinine levels, which can indicate kidney injury. In vitro research has shown that CDK4/6i can also inhibit tubular secretion of creatinine, thereby causing the phenomenon 'pseudo-acute kidney injury (pseudo-AKI)'. The incidence of pseudo-AKI is, however, unknown. We aimed to determine this incidence by assessing cystatin C, a protein filtered in the glomerulus without being subject to tubular secretion, in patients with creatinine increase during CDK4/6i treatment.

METHODS

In this retrospective single-centre cohort study patients with breast cancer who received CDK4/6 inhibitors between January 1st 2017 and December 29th 2023 were screened for the incidence of creatinine increases suggesting potential kidney injury in the first six months of treatment. A significant creatinine increase was defined as 1) a creatinine plasma level of >90 µmol/L in women or >115 µmol/L in men and >10% increase from baseline creatinine plasma level or 2) a creatinine plasma level >1.5 times baseline creatinine or 3) an increase in creatinine plasma level from baseline with >26 µmol/L. Pseudo-AKI was diagnosed if the estimated glomerular filtration rate (eGFR) using cystatin C at the moment of creatinine increase was 1) equal or higher than eGFR using creatinine at baseline and/or 2) at least 25% higher than eGFR using creatinine at the moment of creatinine increase. The primary endpoint was the percentage of patients with pseudo-AKI analysed by means of the binomial probability test.

RESULTS

Of the 234 patients treated with a CDK4/6i, 41 (17.5%) had creatinine levels indicating an AKI. From 22 of these 41 patients, cystatin C could be determined in retrospectively available serum. Pseudo-AKI was found in 16 out of 22 patients (73%, 95% CI 50-89%). In 5 out of 41 patients (12%) the CDK4/6i dose was unjustly adjusted or the drug was stopped due to creatinine increase.

CONCLUSION

Pseudo-AKI has a high incidence in patients treated with CDK4/6i. Determining an eGFR based on the cystatin C value should therefore be considered as the first step when creatinine increases during CDK4/6i treatment.

Final survival results from the PENELOPE-B trial investigating palbociclib versus placebo for patients with high-risk HR+/HER2- breast cancer and residual disease after neoadjuvant chemotherapy-PENELOPE-B

BACKGROUND

The addition of 1 year of palbociclib to endocrine therapy (ET) did not improve invasive disease-free survival (iDFS) compared with placebo in the PENELOPE-B trial. In this article we report the final survival results of the PENELOPE-B trial.

PATIENTS AND METHODS

The PENELOPE-B trial investigated whether adding 1 year of palbociclib to ET in hormone receptor-positive (HR-positive), human epidermal growth factor receptor 2-negative (HER2-negative) breast cancer (BC) patients with residual disease and high relapse risk (clinical and pathological stage + estrogen receptor status and histological grade score ≥3 or 2 and ypN+) after taxane-based neoadjuvant chemotherapy would improve patient survival. Patients (n = 1250) were randomly assigned to receive either palbociclib 125 mg or placebo d1-21 q4w for 13 cycles in addition to ET.

RESULTS

After a median follow-up of 77.8 months, we recorded 225 deaths (108 palbociclib; 117 placebo) with a 6-year overall survival (OS) rate of 82.4% in the palbociclib arm versus 80.3% in the placebo arm (hazard ratio 0.87, 95% confidence interval (CI) 0.67-1.14, P = 0.31). No significant improvement was noted for palbociclib versus placebo for iDFS, distant disease-free survival or locoregional relapse rate, even with longer follow-up. Upon stratified analysis, we found no benefits across major subgroups. However, exploratory post hoc analyses of the lobular BC (LBC) subgroup indicated a trend toward better survival outcomes in favor of palbociclib (hazard ratio 0.45, 95% CI 0.19-1.07, P = 0.062 for OS and hazard ratio 0.52, 95% CI 0.28-0.97, P = 0.035 for iDFS).

CONCLUSION

The study concluded that palbociclib did not significantly improve survival outcomes in the overall population. Exploratory post hoc analyses suggested a trend toward better iDFS outcome in patients with LBC receiving palbociclib.

Synthesis of Amcenestrant (SAR439859): A Copper-Catalyzed Cross-Coupling Reaction as a Sustainable Alternative to Palladium-Catalyzed Suzuki Reaction

A cross-coupling reaction between an enol triflate and an aryl Grignard reagent using a copper catalyst, followed by a deprotection step, a Mitsunobu reaction, and a saponification, allowed for the synthesis of Amcenestrant (SAR439859). This approach, avoiding an expensive and toxic transition metal, is as efficient as the classical route but less expensive for accessing this selective estrogen-receptor degrader (SERD).

Abemaciclib Plus Fulvestrant in Advanced Breast Cancer After Progression on CDK4/6 Inhibition: Results From the Phase III postMONARCH Trial

PURPOSE

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) are the standard first-line treatment for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC); however, disease progression occurs in almost all patients and additional treatment options are needed. Herein, we report outcomes of the postMONARCH trial investigating a switch in ET with/without CDK4/6 inhibition with abemaciclib after disease progression on CDK4/6i.

METHODS

This double-blind, randomized phase III study enrolled patients with disease progression on previous CDK4/6i plus aromatase inhibitor as initial therapy for advanced disease or recurrence on/after adjuvant CDK4/6i + ET. Patients were randomly assigned (1:1) to abemaciclib + fulvestrant or placebo + fulvestrant. The primary end point was investigator-assessed progression-free survival (PFS). Secondary end points included PFS by blinded independent central review, objective response rate (ORR), and safety.

RESULTS

This study randomly assigned 368 patients (abemaciclib + fulvestrant, n = 182 placebo + fulvestrant, n = 186). At the primary analysis (258 events), the hazard ratio (HR) was 0.73 (95% CI, 0.57 to 0.95; nominal P = .017), with median PFS 6.0 (95% CI, 5.6 to 8.6) versus 5.3 (95% CI, 3.7 to 5.6) months and 6-month PFS rates of 50% and 37% in the abemaciclib + fulvestrant and placebo + fulvestrant arms, respectively. These results were supported by BICR-assessed PFS (HR, 0.55 [95% CI, 0.39 to 0.77]; nominal P < .001). A consistent treatment effect was seen across major clinical and genomic subgroups, including with/without ESR1 or PIK3CA mutations. Among patients with measurable disease, investigator-assessed ORR was improved with abemaciclib + fulvestrant versus placebo + fulvestrant (17% v 7%; nominal P = .015). No new safety signals were observed, with findings consistent with the known safety profile of abemaciclib.

CONCLUSION

Abemaciclib + fulvestrant significantly improved PFS after disease progression on previous CDK4/6i + ET in patients with HR+, HER2- ABC, offering an additional targeted therapy option for these patients.

CDK4/6 as a Therapeutic Target in HR+/HER2- Breast Cancer Cells-Current Treatment Status

Breast cancer is the most frequently diagnosed neoplasm in the world. It can be classified into four main subtypes, each of them showing differences in the expression of hormone receptor (HR), human epidermal growth factor receptor 2 (HER2), and in cell metabolism. Since 2015, when The U.S. Food and Drug Administration (FDA) approved the first cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor that regulates the cell cycle, treatment of HR+/HER2- BC has become much more effective. Currently, palbociclib, ribociclib, and abemaciclib are more often used both in combination with endocrine therapy as well as in monotherapy. Their application has been extensively verified in many clinical trials such as PALOMA-1,2,3, MONALEESA-1,2,3,7, and MONARCH-1,2,3, which allowed the verification of differences in their effectiveness, dosage, and adverse effects. Subsequent studies, MonarchE and NATALEE, examined the role of these inhibitors as adjuvant therapy, as well as at verifying their safety. Moreover, dalpiciclib is being investigated in HR+/HER2- BC treatment. This article will summarize clinical efficacy, recommendations, and differences in toxicity profile between palbociclib, ribociclib, and abemaciclib and will also discuss the possibility of using dalpiciclib in the treatment of breast cancer.

Application status and research progress of targeted therapy drugs for hormone receptor-positive breast cancer

Breast cancer (BC) is the most common malignant tumor in women and the leading cause of cancer-related deaths in women. As one of the most common subtypes of breast cancer, patients with hormone receptor-positive (HR+) breast cancer usually experience disease progression over an extended period of time, triggering the search for therapeutic strategies other than endocrine therapy. In recent years, continuous research on various targets has led to dramatic changes in the treatment of hormone receptor-positive breast cancer patients, resulting in prolonged clinical survival. With the redefinition of human epidermal growth factor-2 (HER2) expression, more precise and individualized treatment is possible. This review comprehensively reviews targeted therapies and critical clinical trials for HR+ breast cancer and tracks the latest advances. It also provides valuable insights into the future direction of targeted therapies.

Recent advances in regulating the cell cycle through inhibiting CDKs for cancer treatment

The inhibition of cyclin-dependent kinases (CDKs) is considered a promising strategy for cancer treatment due to their role in cell cycle regulation. However, CDK inhibitors with no selectivity among CDK families have not been approved. A CDK inhibitor with high selectivity for CDK4/6 exhibited significant treatment effects on breast cancer and has become a heavy bomb on the market. Subsequently, resistance gradually decreased the efficacy of selective CDK4/6 inhibitors in breast cancer treatment. In this review, we first introduce the development of selective CDK4/6 inhibitors and then explain the role of CDK2 activation in inducing resistance to CDK4/6 inhibitors. Moreover, we focused on the development of CDK2/4/6 inhibitors and selective CDK2 inhibitors, which will aid in the discovery of novel CDK inhibitors targeting the cell cycle in the future.

Palbociclib exposure in relation to efficacy and toxicity in patients with advanced breast cancer

BACKGROUND

Data on exposure-response or exposure-toxicity relationships of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) are limited and inconclusive. We aimed to investigate whether there is an association between palbociclib exposure and progression-free survival (PFS), adverse events (AEs) and dose reductions.

MATERIALS AND METHODS

Data were retrieved from the prospective, multicentre SONIA trial in which patients with advanced estrogen receptor-positive, human epidermal growth factor receptor 2-negative breast cancer were randomised to receive CDK4/6i treatment in first versus second line. Blood for pharmacokinetics (PK) was taken at day 15 of cycles 1 and 2 during CDK4/6i treatment. Individual trough concentrations and plasma area under the curves of palbociclib were constructed using a population PK model. Associations with palbociclib exposure were tested using Cox regression for PFS and chi-square tests for AEs or dose reductions.

RESULTS

PK data were available for 344 patients. No association between palbociclib exposure and PFS was found. Although patients with higher palbociclib exposure had more dose reductions during their entire CDK4/6i treatment course, this was not reflected by a higher incidence of grade 3-4 AEs in the first 3 months.

CONCLUSION

The absence of an association between palbociclib exposure and PFS and the presence of the association between palbociclib exposure and dose reductions suggest that dose reductions may safely be carried out in case of palbociclib-related toxicity.

Palbociclib plus endocrine therapy versus capecitabine in premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer (Young-PEARL): overall survival analysis of a randomised, open-label, phase 2 study

BACKGROUND

The phase 2 randomised Young-PEARL study demonstrated that palbociclib plus exemestane with ovarian function suppression significantly prolonged progression-free survival compared with capecitabine in premenopausal women with hormone receptor-positive, HER2-negative metastatic breast cancer. Here, we report results of the protocol-specified secondary endpoint of overall survival.

METHODS

Young-PEARL was a multicentre, randomised, open-label, phase 2 study conducted at 14 institutions in South Korea. Premenopausal women aged 19 years or older with histologically confirmed hormone receptor-positive, HER2-negative metastatic breast cancer that recurred or progressed during or after previous tamoxifen treatment, who were aromatase inhibitor naive, and had an Eastern Cooperative Oncology Group performance status of 0-2 were eligible. One previous line of chemotherapy was permitted in the metastatic setting. Eligible patients were randomly assigned (1:1), using block randomisation (block size of two) stratified by previous chemotherapy for metastatic breast cancer and presence of visceral metastasis, to receive either palbociclib (orally, 125 mg per day on a 3-weeks-on, 1-week off schedule) plus exemestane (orally 25 mg daily) with leuprorelin (subcutaneously 3·75 mg on day 1 of each 28-day cycle) or capecitabine (orally, 1250 mg/m2 twice a day on a 2-weeks-on, 1-week-off schedule) until disease progression or unacceptable toxicity). The primary endpoint was progression-free survival. Overall survival was a secondary endpoint. All analyses were done in the modified intention-to-treat population (ie, included all patients randomly assigned to treatment who had at least one post-baseline CT scan and excluded those who did not receive study medication and who had any major violation of the eligible criteria). Safety was assessed in all patients who received any study treatment. This study is registered with ClinicalTrials.gov, NCT02592746, and is now complete.

FINDINGS

Between June 15, 2016, and Dec 10, 2018, 189 patients were enrolled. 184 patients were randomly assigned to the palbociclib plus endocrine therapy group (n=92) or the capecitabine group (n=92), of whom 174 were included in the modified intention-to-treat population (n=90 in the palbociclib plus endocrine therapy group and n=84 in the capecitabine group). All patients were female and ethnicity data were not collected. As of data cutoff (Feb 29, 2024), median follow-up was 54·0 months (IQR 34·1-74·4). Median progression-free survival was 19·5 months (90% CI 14·3-22·2) for palbociclib plus endocrine therapy and 14·0 months (11·7-18·7) for capecitabine (hazard ratio 0·74 [90% CI 0·57-0·98]; one-sided log-rank p=0·036). 52 (58%) of 90 patients in the palbociclib plus endocrine therapy group and 48 (57%) of 84 in the capecitabine group died, with a median overall survival of 54·8 months (95% CI 48·9-77·1) in the palbociclib plus endocrine therapy group versus 57·8 months (46·3-89·2) in the capecitabine group (hazard ratio 1·02 [95% CI 0·69-1·51]; p=0·92). The most common grade 3 or worse adverse event was neutropenia (59 [64%] of 92 in the palbociclib plus endocrine therapy group vs 15 [18%] of 85 in the capecitabine group) . No treatment-related deaths occurred.

INTERPRETATION

With extended follow-up, palbociclib plus exemestane with ovarian function suppression continued to show a significant benefit in progression-free survival compared with capecitabine in premenopausal patients with hormone receptor-positive, HER2-negative metastatic breast cancer who had been previously treated with tamoxifen; however, no improvement in overall survival was seen. Given the progression-free survival benefit, the upfront use of palbociclib plus endocrine therapy is the preferred option for premenopausal women, although a capecitabine-first strategy might be an alternative treatment strategy for maintaining overall survival in resource-limited settings.

FUNDING

Pfizer and Ministry of Health & Welfare, South Korea.

Phase I study of ribociclib (CDK4/6 inhibitor) with spartalizumab (PD-1 inhibitor) with and without fulvestrant in metastatic hormone receptor-positive breast cancer or advanced ovarian cancer

BACKGROUND

Preclinical evidence suggests that cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors enhance antitumor immunity. We conducted a phase I trial of ribociclib (CDK4/6 inhibitor) plus spartalizumab (PD-1 inhibitor) in patients with hormone receptor (HR)-positive/HER2-negative metastatic breast cancer (MBC) or advanced ovarian cancer (AOC). The combination was also evaluated with fulvestrant in MBC.

METHODS

In Cohort A, ribociclib was administered on Days 1-21 (28-day cycle) starting at 400 mg, and spartalizumab at 400 mg on Day 1. Dose escalation was followed by expansion in AOC. Fulvestrant was added (Cohort B) with a safety run-in followed by expansion in MBC. Primary objectives were to determine the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D), and safety and tolerability of the combinations.

RESULTS

33 patients enrolled (n=18, Cohort A; n=15, Cohort B). The RP2D of ribociclib in both cohorts was 600 mg. Treatment-related adverse events in >20% of patients in either cohort were neutropenia, fatigue, anemia, thrombocytopenia, hypertransaminasemia, maculopapular rash, fatigue, and nausea. Hypertransaminasemia occurred in 66.7% (AST) and 46.7% (ALT) of patients in Cohort B, including 46.7% and 40.0%, respectively, of grade 3 or 4 events. Two confirmed partial responses were observed (13.3%) in Cohort B, in patients with low baseline serum thymidine kinase activity, coupled with an increase on-treatment. Peripheral blood flow cytometry across patients demonstrated on-target drug binding with increases in PD-1 occupancy and activated CD8+ T cells during treatment, irrespective of response. PD-L1-positivity, tumor-infiltrating lymphocytes, or tumor mutational burden did not correlate with progression-free survival (PFS). Several copy-number variations detected with next-generation sequencing correlated with PFS.

CONCLUSIONS

Ribociclib with spartalizumab and fulvestrant showed limited efficacy and elevated hepatotoxicity, precluding further development. Correlative analyses revealed treatment-induced immunological effects, and genomic alterations associated with PFS.

Hepatic adverse events with CDK4/6 inhibitors: a systematic review combining meta-analysis and FAERS database

BACKGROUND

Cell-cycle protein-dependent kinase 4 and 6 inhibitors (CDK4/6is) in combination with endocrine therapy (ET) are widely used in patients with early and advanced breast cancer (BC). CDK4/6is also lead to numerous side effects. This study aims to elucidate the relationship between CDK4/6is and hepatotoxicities.

RESEARCH DESIGN AND METHODS

As of 31 March 2024, we conducted a systematic search of PubMed, Embase, and the Cochrane Library databases, as well as several oncology conference proceedings. We included 20 randomized controlled trials (RCTs) with 24,342 breast cancer (BC) patients and 400 cases from the FDA Adverse Event Reporting System (FAERS). Fixed-effect and random-effect models were used to calculate odds ratios (ORs) of hepatotoxicity in the RCTs, while Reporting Odds Ratios (RORs) were calculated for the FAERS data.

RESULTS

Overall, CDK4/6 inhibitors (CDK4/6is) were associated with significant hepatotoxicities compared to controls (OR = 1.76, 95%CI 1.40-2.22, I2 = 75%). Palbociclib, ribociclib, and abemaciclib exhibited significant hepatotoxicities, while dalpiciclib did not. FAERS data showed significant liver enzyme and organ toxicity signals for ribociclib and abemaciclib but not for palbociclib.

CONCLUSIONS

CDK4/6is increase the risk of hepatotoxicities in patients with BC. Palbociclib, ribociclib, and abemaciclib caused liver damage, while dalpiciclib did not. The most common manifestations were elevated ALT and AST levels.

Adverse event profiles of CDK4/6 inhibitors: a disproportionality analysis of the FDA Adverse Event Reporting System (FAERS) database

BACKGROUND

The safety profile of CDK4/6 inhibitors has not yet been systemically analysed in the real world. This study aimed to provide a comprehensive understanding of AEs associated with CDK4/6 inhibitors using the FAERS database.

METHODS

FAERS data (2014Q1 to 2022Q4) were searched for reports of all FDA-approved CDK4/6 inhibitors across all indications. We used the SMQ generalized search AEs on the PT level. Disproportionality analysis was used to detect safety signals by calculating RORs.

RESULTS

Within the standardized MedDRA queries, significant safety signals were found, including those for palbociclib [haematopoietic leukopenia, erythropenia], ribociclib [haematopoietic leukopenia , conduction defects], and abemaciclib [eosinophilic pneumonia, dehydration]. For AEs at the PT level, we found several significant blood and lymphatic system disorders for both palbociclib and ribociclib, such as abnormal full blood count and decreased white blood cell count for palbociclib and anisocytosis, neutropenia for ribociclib. Palbociclib also had high RORs for pseudocirrhosis, stomatitis, oral pain, and alopecia, while ribociclib had high RORs for electrocardiogram PR shortened, sinus arrhythmia, and blood bilirubin abnormal. However, the RORs were significant for abemaciclib in terms of diarrhoea, vena cava thrombosis, thrombophlebitis migrans and pneumonitis.

CONCLUSION

CDK4/6 inhibitors differed in their safety profile reports.

The Impact of Progesterone Receptor Status on Survival Outcomes in Metastatic Breast Cancer Patients Treated with First-Line CDK4/6 Inhibitors

BACKGROUND/OBJECTIVES

CDK4/6 inhibitors have changed the landscape of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (BC) management. It is essential to identify predictive and prognostic factors for the efficacy of CDK4/6 inhibitors. We aimed to investigate the differences in characteristics and outcomes of patients receiving first-line CDK4/6 inhibitors according to PgR status.

METHODS

This multicenter retrospective study included 351 patients treated with first-line CDK 4/6 inhibitors for HR-positive/HER2-negative metastatic BC. Patients were categorized based on their PgR expression levels, including the PgR-low (<20%) and PgR-high (≥20%) groups, and baseline characteristics, treatment responses, and survival outcomes were analyzed.

RESULTS

The median age was 57 years (range: 26-85). A total of 99 patients were premenopausal, and 252 patients were postmenopausal. There were 115 (32.8%) patients in the PgR-low group, while 236 (67.2%) were in the PgR-high group. The majority of patients (56.7%) presented with de novo metastatic disease. Visceral metastases presented in 44.2% of patients. Low PgR expression was significantly associated with lower estrogen receptor levels (p = 0.031), elevated Ki-67 levels (p = 0.002), a higher incidence of visceral metastases (p = 0.035), and recurrent disease (p = 0.019). In the multivariate analysis, low PgR expression was a significant independent predictor of worse progression-free survival (PFS) and overall survival (OS).

CONCLUSIONS

We demonstrated that low PgR expression is independently and significantly correlated with shorter PFS and OS. These findings support low PgR expression as a valuable prognostic biomarker in metastatic BC patients treated with first-line CDK4/6 inhibitors.

Evaluation of Dose Reduction Factors and Impact on Progression-Free Survival in Patients Treated with CDK 4/6 Inhibitors

Introduction: CDK 4/6 inhibitors are effectively utilized among patients with hormone-positive, HER-2-negative metastatic breast cancer. The dose reduction for these patients varies between 35% and 57% across multiple trials. We aim to clarify the characteristics of patients who had dosage reduction and the effect of this reduction on survival outcomes. Materials and Methods: The study was designed as a retrospective, multicenter study. Patients who received CDK 4/6 inhibitors in the first-line and subsequent treatment settings were grouped based on dose reductions. Progression-free survival was compared between these groups, and factors influencing dose reduction were analyzed. Results: Multivariate logistic regression study demonstrated that patients aged 65 and older, with a Charlson CI score of 2 or higher, having metastases in three or more sites, and classed as normal weight, had greater dosage reductions. Dose reduction had no impact on progression-free survival (PFS) (p = 0.114 for first-line treatment, p = 0.528 for second and subsequent-line treatment; p > 0.05). Conclusions: Regarding the absence of disparity in progression-free survival between patients with dose reduction and those without, dose reduction should not be avoided in certain patient groups to ensure therapy continuity and mitigate potential adverse effects.

Cyclin-dependent kinase 4/6 inhibitor-associated pulmonary toxicity: a disproportionality analysis from 2015 to 2023 based on the FAERS database

OBJECTIVES

This study aimed to describe the pulmonary toxicity of cyclin-dependent kinase 4/6 inhibitors (CDK 4/6 inhibitors) (palbociclib, ribociclib, and abemaciclib) in patients being treated for breast cancer using the Food and Drug Administration Adverse Event Reporting System (FAERS) database.

RESEARCH DESIGN AND METHODS

Disproportionality analysis was performed to assess pulmonary toxicity associated with CDK 4/6 inhibitors. Clinical characteristics, onset time, sensitivity analysis, subgroup analyses, drug combinations, comorbidities, and co-reported events were performed.

RESULTS

Out of 83,505 CDK 4/6 inhibitor-related adverse events (AEs) documented in the FAERS database during the study period, 437 cases of pneumonitis, 555 cases of pulmonary edema, and 181 cases of pulmonary thrombosis related to CDK 4/6 inhibitors were analyzed. Pneumonitis and pulmonary thrombosis had the strongest signal strength in abemaciclib; pulmonary edema had the strongest signal strength in ribociclib. The median latency for pneumonitis, pulmonary edema, and pulmonary thrombosis was 66-173.5 days, 27-131 days, and 68-279 days, respectively. Pulmonary toxicity is statistically significant disproportionality in females as well as in patients over 60 years old.

CONCLUSION

Abemaciclib was most strongly associated with pneumonitis and pulmonary thrombosis. Ribociclib was most strongly associated with pulmonary edema. The correlation with pulmonary toxicity was, in descending order, abemaciclib, ribociclib, and palbociclib.

Survival Following CDK4/6 Inhibitor Therapy for Hormone Receptor-Positive, ERBB2-Negative Metastatic Breast Cancer

Importance

Endocrine therapy (ET) combined with cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) agents is the standard first-line treatment for patients with hormone receptor-positive, ERBB2 (formerly HER2 or HER2/neu)-negative metastatic breast cancer. However, optimal therapy after tumor progression to ET plus CDK4/6i remains unclear.

Objective

To evaluate progression-free survival (PFS) and overall survival (OS) in the clinical practice setting in patients with hormone receptor-positive, ERBB2-negative metastatic breast cancer following progression with ET plus CDK4/6i.

Design, Setting, and Participants

The multicenter retrospective cohort study included 506 patients diagnosed with hormone receptor-positive, ERBB2-negative metastatic breast cancer between April 22, 2015, and January 31, 2023, and who received ET-based or chemotherapy (CT)-based treatment following progression during ET plus CDK4/6i. Outcomes were analyzed based on treatment type, clinicopathologic features, and the duration of prior CDK4/6i therapy.

Main Outcomes and Measures

The primary end point was PFS in the clinical practice setting, defined as the time between the initiation of the first systemic treatment on tumor progression to ET plus CDK4/6i treatment and the detection of disease progression or patient death from any cause. The secondary end point was OS in the clinical practice setting, defined as the time interval between tumor progression during ET plus CDK4/6i treatment and patient death from any cause.

Results

In 506 women (median age at diagnosis, 52.4 [IQR, 44.6-62.8] years) diagnosed with hormone receptor-positive, ERBB2-negative metastatic breast cancer progressing during ET plus CDK4/6i, independent factors associated with poorer PFS outcomes were visceral metastases (hazard ratio [HR], 1.45; 95% CI, 1.17-1.80; P = .008) and de novo metastatic disease (HR, 1.25; 95% CI, 1.01-1.54; P = .04). A longer duration of CDK4/6i therapy (OS HR, 0.55; 95% CI, 0.41-0.73; P < .001) and an older age (PFS HR, 0.99; 95% CI 0.98-1.00; P = .03) were associated with better outcomes. Compared with oral CT, both intravenous CT- and ET-based treatments were associated with shorter PFS (intravenous CT: hazard ratio [HR], 1.45; 95% CI, 1.11-1.89; P = .006; everolimus plus exemestane: HR, 1.38; 95% CI, 1.06-1.78; P = .02; ET only: HR, 1.38; 95% CI, 1.05-1.89; P = .02). A duration of CDK4/6i treatment exceeding 12 months was associated with longer OS (HR, 0.55; 95% CI, 0.41-0.73; P < .001). Among patients with visceral metastases, intravenous CT was associated with shorter OS compared with oral CT (HR, 1.52; 95% CI, 1.03-2.24; P = .04).

Conclusions and Relevance

In this cohort study, the duration of tumor control achieved with CDK4/6i-based therapy and the presence of visceral metastases emerged as key factors that may affect treatment decision. Oral CT may offer potential benefits for specific patient subgroups.

Efficacy and Safety of CDK4/6 Inhibitors: A Focus on HR+/HER2- Early Breast Cancer

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have revolutionized the treatment of hormone-receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer, and are now also established agents in the treatment of high-risk and intermediate-risk HR+ early breast cancer. Several strategies regarding CDK4/6i combinations or continuation beyond progression have been successfully evaluated in the metastatic setting, and are considered a standard of care. Mechanism of action of and resistance mechanisms against CDK4/6i in addition to endocrine resistance represent an important research topic, important for the treatment of HR+ breast cancer. Clinically, CDK4/6i are efficient substances that are usually well tolerated. However, side effects differing between the substances have been reported, and might lead to treatment discontinuation, including in the early disease setting. In the adjuvant setting, the addition of palbociclib to standard endocrine treatment has not improved outcomes, whereas large randomized phase III trials have demonstrated significant disease-free survival benefit for the addition of ribociclib (NATALEE trial) and abemaciclib (monarchE trial). Patient selection, treatment duration, endocrine backbone therapy, and other study details differ between these pivotal trials. This review focuses on both the scientific background as well as all available clinical data of CDK4/6i, with particular emphasis on their use in early breast cancer.

Current and Novel Treatment Options in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer

Metastatic breast cancer (mBC) remains an incurable disease, and most patients will experience disease progression during their treatment course. Although endocrine therapy remains the mainstay of treatment for hormone receptor-positive/human epidermal growth factor receptor 2-negative mBC, significant progress has been and continues to be made in the treatment of this BC subtype. The discovery of molecular markers, mutations in key cellular pathways, and genomic signatures have led to the development of novel and targeted agents, such as antibody-drug conjugates, oral selective estrogen receptor downregulators, and inhibitors of the PI3K/AKT/mTOR pathway. This has resulted in significant improvements in the survival and quality of life of patients. With the increasing number of treatment options for patients, appropriate drug sequencing remains a challenge. Treatment discussions should involve patient-physician shared decision making, with consideration of genomic data, previous lines of therapy, side effect profiles, and clinical trial enrollment.

Targeting the mitotic kinase NEK2 enhances CDK4/6 inhibitor efficacy by potentiating genome instability

Selective inhibitors that target cyclin-dependent kinases 4 and 6 (CDK4/6i) are approved by the U.S. Food and Drug Administration (FDA) for treatment of a subset of breast cancers and are being evaluated in numerous clinical trials for other cancers. Despite this advance, a subset of tumors are intrinsically resistant to these drugs and acquired resistance is nearly inevitable. Recent mechanistic evidence suggests that in addition to stalling the cell cycle, the antitumor effects of CDK4/6i involve the induction of chromosomal instability (CIN). Here, we exploit this mechanism by combining CDK4/6i with other instability-promoting agents to induce maladaptive CIN and irreversible cell fates. Specifically, dual targeting of CDK4/6 and the mitotic kinase NEK2 in vitro drives centrosome amplification and the accumulation of CIN that induces catastrophic mitoses, cell cycle exit, and cell death. Dual targeting also induces CIN in vivo and significantly decreases mouse tumor volume to a greater extent than either drug alone, without inducing overt toxicity. Importantly, we provide evidence that breast cancer cells are selectively dependent on NEK2, but nontransformed cells are not, in contrast with other mitotic kinases that are commonly essential in all cell types. These findings implicate NEK2 as a potential therapeutic target for breast cancer that could circumvent the dose-limiting toxicities that are commonly observed when blocking other mitotic kinases. Moreover, these data suggest that NEK2 inhibitors could be used to sensitize tumors to FDA-approved CDK4/6i for the treatment of breast cancers, improving their efficacy and providing a foundation for expanding the patient population that could benefit from CDK4/6i.

Dual Inhibition of CDK4/6 and CDK7 Suppresses Triple-Negative Breast Cancer Progression via Epigenetic Modulation of SREBP1-Regulated Cholesterol Metabolism

Inhibitors targeting cyclin-dependent kinases 4 and 6 (CDK4/6) to block cell cycle progression have been effective in treating hormone receptor-positive breast cancer, but triple-negative breast cancer (TNBC) remains largely resistant, limiting their clinical applicability. The study reveals that transcription regulator cyclin-dependent kinase7 (CDK7) is a promising target to circumvent TNBC's inherent resistance to CDK4/6 inhibitors. Combining CDK4/6 and CDK7 inhibitors significantly enhances therapeutic effectiveness, leading to a marked decrease in cholesterol biosynthesis within cells. This effect is achieved through reduced activity of the transcription factor forkhead box M1 (FOXM1), which normally increases cholesterol production by inducing SREBF1 expression. Furthermore, this dual inhibition strategy attenuates the recruitment of sterol regulatory element binding transcription factor 1 (SREBP1) and p300 to genes essential for cholesterol synthesis, thus hindering tumor growth. This research is corroborated by an in-house cohort showing lower survival rates in TNBC patients with higher cholesterol production gene activity. This suggests a new treatment approach for TNBC by simultaneously targeting CDK4/6 and CDK7, warranting additional clinical trials.

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i): Mechanisms of resistance and where to find them

CDK4/6 inhibitors (CDK4/6i) have significantly impacted on the treatment of HR + HER2 negative (HER2-) metastatic breast cancer (BC) when combined with endocrine therapy. Nonetheless, despite significant research efforts, the mechanisms of de novo and acquired resistance to CDK4/6i have not yet been fully elucidated, highlighting the need for a deeper understanding of these process. Additionally, the importance of dissecting CDK4/6i resistance from endocrine resistance for personalized treatment is increasingly recognized. Liquid biopsy has emerged as a minimally invasive tool for identifying circulating biomarkers of resistance through the integration of multiparametric and dynamic assessments that encompass ctDNA, CTCs, exosomes, and epigenetic ctDNA alterations, representing a promising perspective for the clinical characterization of treatment resistance and guiding post-progression strategies to improve patient outcomes. Aim of this review is summarize potential mechanisms of CDK4/6i resistance, along with the advantages of using liquid biopsy to identify resistance biomarkers in HR+/HER2- MBC patients treated with CDK 4/6 inhibitors.

Impact of low HER2 expression on response to CDK4/6 inhibitor treatment in advanced HR + /HER2- breast cancer: a multicenter real-world data analysis

PURPOSE

CDK4/6 inhibitors (CDK4/6i) represent the first-line therapy approach of choice for patients with hormone receptor-positive, HER2-negative advanced breast cancer (HR + /HER-ABC). Approximately 50% of HR + /HER2-ABC displays low HER2 expression (HER2 low). Recent data emerging from the DESTINY-Breast04 trial demonstrated practice-changing efficacy of the antibody-drug conjugate trastuzumab deruxtecan (T-DXd) in patients with low HER2 expression. Here, we aimed to analyze the impact of low HER2 expression on CDK4/6i therapy response in a well-characterized multicenter HR + /HER-ABC cohort.

METHODS

Patients diagnosed with HR + /HER2-ABC who were treated with CDK4/6i in clinical routine between November 2016 and December 2020 at four certified German Breast Cancer Centers were retrospectively identified. The cohort was stratified according to graduation of positivity in HER2 immunohistochemistry (IHC; HER2 zero = IHC score 0 and HER2 low = IHC score 1 + , 2 + /fluorescence in situ hybridization negative). Subgroups were analyzed with regard to progression-free survival (PFS) following CDK4/6i initiation.

FINDINGS

The study cohort comprised n = 448 patients. For n = 311 patients, HER2 status from the metastatic site was available. n = 91 (29.3%) cases were HER2 zero and n = 220 cases (70.7%) were HER2 low. There was no significant difference in PFS between the two groups (PFS: 17 months versus 18 months, log-rank p = 0.42). Further, we examined the influence of HER2 expression changes between primary and metastatic tissue (n = 171; HER2 gain/HER2 loss/HER2 stable expression) on CDK4/6i treatment response. Again, there was no significant difference between these three groups, respectively (PFS: 16 months versus 13 months versus 17 months, log-rank p = 0.86).

CONCLUSIONS

In our analysis, HER2 status did not have a significant impact on treatment response to CDK4/6i.

Beyond Hormone Receptors: liquid biopsy tools to unveil new clinical meanings and empower therapeutic decision-making in Luminal-like metastatic breast cancer

Immunohistochemical (IHC) tissue profiling is a standard practice in the management of metastatic breast cancer (mBC), that enables the identification of distinct biological phenotypes based on hormone receptors' expression. Luminal-like tumors primarily benefit from a first line treatment strategy combining endocrine therapy and cyclin-dependent kinase 4/6 inhibitors. However, IHC analyses necessitate invasive procedures and may encounter technical and interpretational challenges. In the current era of precision medicine, liquid biopsy holds potential to provide clinicians with additional insights into disease biology, including mechanisms underlying endocrine resistance and disease progression. Several liquid-based biomarkers are entering clinical practice and hold prognostic and predictive values in Luminal-like mBC, while many others are currently being investigated. The present work aims to summarize the current evidence regarding the clinical meanings of hormone receptors and their downstream molecular pathways, alongside their implications for therapeutic decision-making in Luminal-like mBC.