Real-world treatment patterns and clinical outcomes in patients treated with eribulin after prior phosphoinositide 3-Kinase inhibitor treatment for metastatic breast cancer

PURPOSE

In 2010, the US Food and Drug Administration approved eribulin for the treatment of metastatic breast cancer (MBC). Since then, the treatment landscape has evolved with many new therapy classes, a more recent one being the small molecule inhibitors of phosphoinositide 3 kinase (PI3K). We sought to characterize the treatment patterns and clinical outcomes of patients with MBC who received eribulin following prior treatment with a PI3K inhibitor.

METHODS

A retrospective cohort study based on medical record review included MBC patients who initiated eribulin between March 2019 and September 2020 following prior treatment with a PI3K inhibitor was conducted. Patient demographics, treatment characteristics, and clinical outcomes were analyzed descriptively. Real-world progression-free survival (rwPFS) and overall survival (OS) were estimated from the initiation of eribulin therapy using Kaplan-Meier analyses.

RESULTS

82 eligible patients were included. Patients' median age at eribulin initiation was 62 years; 86.5% had hormone receptor-positive, human epidermal growth factor receptor 2-negative tumors. Eribulin was most often administered in the second or third line (82.9%) in the metastatic setting. Best overall response on eribulin was reported as complete or partial response in 72% of the patients. The median rwPFS was 18.9 months (95% confidence interval [CI], 12.4-not estimable); median OS was not reached. The estimated rwPFS and OS rates at 12 months were 63.3% (95% CI, 50.5-73.7) and 82.6% (95% CI, 72.4-89.3), respectively.

CONCLUSION

Our real-world study suggests that eribulin may be a potential treatment option for MBC patients who fail a prior PI3K inhibitor.

Therapies for the Treatment of Advanced/Metastatic Estrogen Receptor-Positive Breast Cancer: Current Situation and Future Directions

The hormone receptor-positive (HR+) type is the most frequently identified subtype of breast cancer. HR+ breast cancer has a more positive prognosis when compared to other subtypes, such as human epidermal growth factor protein 2-positive disorder and triple-negative disease. The advancement in treatment outcomes for advanced HR+ breast cancer has been considerably elevated due to the discovery of cyclin-dependent kinase 4/6 inhibitors and their combination effects with endocrine therapy. However, despite the considerable effectiveness of tamoxifen, a selective estrogen receptor modulator (SERMs), and aromatase inhibitors (AI), the issue of treatment resistance still presents a significant challenge for HR+ breast cancer. As a result, there is a focus on exploring new therapeutic strategies such as targeted protein degradation and covalent inhibition for targeting ERα. This article discusses the latest progress in treatments like oral selective ER degraders (SERDs), complete estrogen receptor antagonists (CERANs), selective estrogen receptor covalent antagonists (SERCAs), proteolysis targeting chimera (PROTAC) degraders, and combinations of CDK4/6 inhibitors with endocrine therapy. The focus is specifically on those compounds that have transitioned into phases of clinical development.

An emerging generation of endocrine therapies in breast cancer: a clinical perspective

Anti-estrogen therapy is a key component of the treatment of both early and advanced-stage hormone receptor (HR)-positive breast cancer. This review discusses the recent emergence of several anti-estrogen therapies, some of which were designed to overcome common mechanisms of endocrine resistance. The new generation of drugs includes selective estrogen receptor modulators (SERMs), orally administered selective estrogen receptor degraders (SERDs), as well as more unique agents such as complete estrogen receptor antagonists (CERANs), proteolysis targeting chimeric (PROTACs), and selective estrogen receptor covalent antagonists (SERCAs). These drugs are at various stages of development and are being evaluated in both early and metastatic settings. We discuss the efficacy, toxicity profile, and completed and ongoing clinical trials for each drug and highlight key differences in their activity and study population that have ultimately influenced their advancement.

Analysis of PIK3CA Mutation Concordance and Frequency in Primary and Different Distant Metastatic Sites in Breast Cancer

PURPOSE

The purpose of this study was to investigate the concordance rate of PIK3CA mutations between primary and matched distant metastatic sites in patients with breast cancer and to verify whether there are differences in the frequency of PIK3CA hotspot mutations depending on the metastatic sites involved.

MATERIALS AND METHODS

Archived formalin-fixed paraffin-embedded (FFPE) specimens of primary breast and matched distant metastatic tumors were retrospectively obtained for 49 patients. Additionally, 40 archived FFPE specimens were independently collected from different breast cancer metastatic sites, which were limited to three common sites: the liver, brain, and lung. PIK3CA mutations were analyzed using droplet digital PCR, including hotspots involving exons 9 and 20.

RESULTS

After analysis of 49 breast tumors with matched metastasis sites, 87.8% showed concordance in PIK3CA mutation status. According to PIK3CA hotspot mutation testing in 89 cases of breast cancer metastatic sites, the proportion of PIK3CA mutations at sites of metastasis involving the liver, brain, and lung was 37.5%, 28.6%, and 42.9%, respectively, which did not result in statistical significance.

CONCLUSION

The high concordance of PIK3CA mutation status between primary and matched metastasis sites suggests that metastatic sites, regardless of the metastatic organ, could be considered sample sources for PIK3CA mutation testing for improved therapeutic strategies in patients with metastatic breast cancer.

Computational Design of Phosphatidylinositol 3-Kinase Inhibitors

One of the most sought-after therapeutic targets for treating human cancers is the phosphoinositide 3-kinase; PI3k is an integral part of the PI3K/protein kinase B signaling arcade. This pathway is frequently activated in malignancies. Drug resistance and dose-limiting adverse effects are currently associated challenges with the existing anticancer chemotherapy. Therefore, in this research, a series of pyrimidine derivatives were designed and evaluated against human PI3K by using molecular docking analysis. The docking results were further verified by molecular dynamic simulation, which analyzed the strength of the macromolecular complex with respect to time. Compounds IV and XIV were found to be the most potent inhibitors of the human PI3K receptor with a high degree of stability within the active site of the target receptor for a timeframe of 50 ns. Thus, both of these compounds could be important drug candidates for the development of PI3K inhibitors as a prospective anticancer agent.

The role of HER2 alterations in clinicopathological and molecular characteristics of breast cancer and HER2-targeted therapies: a comprehensive review

Breast cancer (BC) is the most common malignancy in women and one of the leading causes of cancer mortality, despite significant treatment advancements over the last decades. Human epidermal growth factor receptor-2 (HER2) is a member of the ERBB family of receptor tyrosine kinases which have long been known to mediate cancer cell growth and invasion through constitutive activation of oncogenic downstream signaling, such as PI3K/Akt/mTOR and MAPK. Overexpression/amplification of HER2 in various tumors, especially BC, offers the possible therapeutic potential for target therapies. HER2-targeted therapies, either with a combination of chemotherapy or through multi-anti-HER2 therapies without chemotherapy, have significantly improved the prognosis of HER2-positive tumors. In recent years, novel anti-HER2 agents and combination therapies have garnered much attention, especially for heavily treated advanced or metastatic BCs. HER2-positive BC is biologically a heterogeneous group depending on HER2 activation mechanisms, hormone receptor status, genome variations, tumor heterogeneity, and treatment resistance, which affect the treatment benefit and patients' outcomes. This review will discuss HER2 alternations (gene amplification or receptor overexpression) in BC, their correlation with clinicopathological characteristics and molecular characteristics, and HER2-based therapies in tumors with HER2 overexpression/amplification.

PIK3CA mutation status, progression and survival in advanced HR + /HER2- breast cancer: a meta-analysis of published clinical trials

Background

Approximately 40% of hormone receptor positive/human epidermal receptor 2 negative (HR + /HER2-) metastatic breast cancer (mBC) patients harbor phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA) mutations. However, associations between PIK3CA mutation status and clinical outcomes among patients with HR + /HER2- mBC have been heterogeneous across clinical trials. This meta-analysis was conducted to survey recently available trial data to assess the prognostic effects of PIK3CA among patients with HR + /HER2- mBC. 

Methods

Randomized clinical trials reporting progression-free survival (PFS) or overall survival (OS) stratified by PIK3CA status in HR + /HER2- mBC were identified via systematic literature review. Trial arms receiving phosphatidylinositol 3-kinase (PI3K)-targeted therapies were excluded. Meta-regression analysis was used to estimate the association between PIK3CA status and PFS and OS among included studies.

Results

The analyzed data included 3,219 patients from 33 study arms across 11 trials (PIK3CA mutated: 1,386, wild type: 1,833). PIK3CA mutation was associated with shorter median PFS (difference [95% CI] (months): -1.8 [-3.4, -0.1], I² = 35%) and shorter median OS (-8.4 [-13.4, -3.5], I² = 58%, N = 1,545). Findings were similar for PFS rates at 6 months (odds ratio [95% CI]: 0.74 [0.59, 0.94], I² = 42%, N = 3,160) and 12 months (0.76 [0.59, 0.99], I² = 42%, N = 2,468) and directionally consistent but not statistically significant at 18 months (N = 1,726).

Conclusions

Pooling evidence across multiple studies, PIK3CA mutation was associated with shorter PFS and OS. These findings suggest a negative prognostic value of PIK3CA mutations in patients with HR + /HER2- mBC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10078-5.

Resistance Mechanisms to Combined CDK4/6 Inhibitors and Endocrine Therapy in ER+/HER2- Advanced Breast Cancer: Biomarkers and Potential Novel Treatment Strategies

The introduction of CDK4/6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) has revolutionized the treatment landscape for patients with estrogen receptor-positive (ER+) advanced breast cancer (ABC) and has become the new standard treatment. However, resistance to this combined therapy inevitably develops and represents a major clinical challenge in the management of ER+ ABC. Currently, elucidation of the resistance mechanisms, identification of predictive biomarkers, and development of novel effective combined targeted treatments to overcome the resistance are active areas of research. Given the heterogeneity of the resistance mechanisms towards combined CDK4/6i and ET, identification of a single universal predictive biomarker of resistance is unlikely. Novel approaches are being explored, including examination of multiple genetic alterations in circulating cell-free tumor DNA in liquid biopsies from ABC patients with disease progression on combined CDK4/6i and ET treatment. Here, we review the molecular basis of the main known resistance mechanisms towards combined CDK4/6i and ET and associated potential biomarkers. As inhibiting key molecules in the pathways driving resistance may play an important role in the selection of therapeutic strategies for patients who experience disease progression on combined CDK4/6i and ET, we also review preclinical and early phase clinical data on novel combination therapies for these patients.

The Place of Chemotherapy in The Evolving Treatment Landscape for Patients With HR-positive/HER2-negative MBC

Endocrine therapy (ET) for the treatment of patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR-positive/HER2-negative) metastatic breast cancer (MBC) has changed markedly over recent years with the emergence of new ETs and the use of molecularly targeted agents. Cytotoxic chemotherapy continues, however, to have an important role in these patients and it is important to maximize its efficacy while minimizing toxicity to optimize outcomes. This review examines current HR-positive/HER2-negative MBC clinical guidelines and addresses key questions around the use of chemotherapy in the face of emerging therapeutic options. Specifically, the indications for chemotherapy in patients with HR-positive/HER2-negative MBC and the choice of optimal chemotherapy are discussed.

Combined inhibition of DDR1 and CDK4/6 induces synergistic effects in ER-positive, HER2-negative breast cancer with PIK3CA/AKT1 mutations

Molecular alterations in the PI3K/AKT pathway occur frequently in hormone receptor-positive breast tumors. Patients with ER-positive, HER2-negative metastatic breast cancer are often treated with CDK4/6 inhibitors such as palbociclib in combination with endocrine therapy. Although this is an effective regimen, most patients ultimately progress. The purpose of this study was identifying synthetic lethality partners that can enhance palbociclib's antitumor efficacy in the presence of PIK3CA/AKT1 mutations. We utilized a barcoded shRNA library to determine critical targets for survival in isogenic MCF7 cells with PIK3CA/AKT1 mutations. We demonstrated that the efficacy of palbociclib is reduced in the presence of PIK3CA/AKT1 mutations. We also identified that the downregulation of discoidin domain receptor 1 (DDR1) is synthetically lethal with palbociclib. DDR1 knockdown and DDR1 pharmacological inhibitor decreased cell growth and inhibited cell cycle progression in all cell lines, while enhanced the sensitivity of PIK3CA/AKT1 mutant cells to palbociclib. Combined treatment of palbociclib and 7rh further induced cell cycle arrest in PIK3CA/AKT1 mutant cell lines. In vivo, 7rh significantly enhanced palbociclib's antitumor efficacy. Our data indicates that DDR1 inhibition can augment cell cycle suppressive effect of palbociclib and could be effective strategy for targeted therapy of ER-positive, HER2-negative breast cancers with PI3K pathway activation.

Precision medicine in breast cancer: From clinical trials to clinical practice

INTRODUCTION

Breast cancer (BC) is the most common cancer in women and, despite the undeniable improvements in the outcome of these patients obtained in the last decade, the discovery and the validation of new actionable molecular targets represent a priority. ESCAT permits to rank molecular alterations in different classes according to their evidence of actionability in a specific cancer type, assisting clinicians in their therapeutical decisions. MAIN: ERBB2, PIK3CA and germline BRCA1/2 alterations are biomarkers prospectively validated in BC, driving the selection of targeted therapies, and are therefore classified in the highest level of evidence (Ia). Agnostic biomarkers, namely microsatellite instability, NTRK fusions and high tumor mutational burden, demonstrated similar activity across different tumor types and are consequently ranked in tier Ic. In tier II are classified alterations that still need confirmatory prospective studies but for which evidence of efficacy is available. Somatic BRCA1/2 mutations, germline PALB2 mutations, HER2-low expression, ERBB2 mutations, PTEN deletions, AKT1 mutations, ESR1 resistance mutations satisfy the requirements to be classified in this tier. In tier III are ranked various molecular alterations for which there is evidence of actionability in other tumors (IIIa) or that have similar functional impact in the same gene or pathway of a tier I alteration, without clinical data (IIIb). In tier IV are listed the molecular alterations for which only preclinical studies are available.

CONCLUSION

In this review we report the most relevant molecular targets in BC, ordered pursuant to their pathway and classified in concordance with ESCAT.

PI3K Inhibitors in Cancer: Clinical Implications and Adverse Effects

The phospatidylinositol-3 kinase (PI3K) pathway is a crucial intracellular signaling pathway which is mutated or amplified in a wide variety of cancers including breast, gastric, ovarian, colorectal, prostate, glioblastoma and endometrial cancers. PI3K signaling plays an important role in cancer cell survival, angiogenesis and metastasis, making it a promising therapeutic target. There are several ongoing and completed clinical trials involving PI3K inhibitors (pan, isoform-specific and dual PI3K/mTOR) with the goal to find efficient PI3K inhibitors that could overcome resistance to current therapies. This review focuses on the current landscape of various PI3K inhibitors either as monotherapy or in combination therapies and the treatment outcomes involved in various phases of clinical trials in different cancer types. There is a discussion of the drug-related toxicities, challenges associated with these PI3K inhibitors and the adverse events leading to treatment failure. In addition, novel PI3K drugs that have potential to be translated in the clinic are highlighted.

Innovations in targeted therapies for triple negative breast cancer

PURPOSE OF REVIEW

Triple negative breast cancer (TNBC) is defined by a lack of targets, namely hormone receptor (HR) expression and human epidermal growth factor receptor 2 amplification. Cytotoxic chemotherapy remains the mainstay of treatment. Though TNBC constitutes approximately 10-15% of breast cancer, it is disproportionally lethal, but it is hoped that outcomes will improve as targetable oncogenic drivers are identified.

RECENT FINDINGS

Translational work in TNBC has focused on subsets defined by defects in homologous recombination repair, immune cell infiltration, or programmed death ligand receptor 1 expression, an over-active phosphoinositide-3 kinase pathway, or expression of androgen receptors. Though not specific to TNBC, the novel cell surface antigen trophoblast antigen 2 has also been identified and successfully targeted. This work has led to Food and Drug Administration approvals for small molecule poly-ADP-ribosyl polymerase inhibitors in patients with deleterious germline mutations in BRCA1 or BRCA2, the combination of nab-paclitaxel with immune checkpoint inhibitor antibodies in the first-line metastatic setting for programmed death ligand receptor 1+ TNBC, and use of the antibody-drug conjugate sacituzumab govitecan in the later-line metastatic setting.

SUMMARY

Identification of targetable oncogenic drivers in TNBC is an area of intense cancer biology research, hopefully translating to new therapies and improved outcomes.

Recent Discoveries of Macromolecule- and Cell-Based Biomarkers and Therapeutic Implications in Breast Cancer

Breast cancer is the most commonly diagnosed cancer type and the leading cause of cancer-related mortality in women worldwide. Breast cancer is fairly heterogeneous and reveals six molecular subtypes: luminal A, luminal B, HER2+, basal-like subtype (ER−, PR−, and HER2−), normal breast-like, and claudin-low. Breast cancer screening and early diagnosis play critical roles in improving therapeutic outcomes and prognosis. Mammography is currently the main commercially available detection method for breast cancer; however, it has numerous limitations. Therefore, reliable noninvasive diagnostic and prognostic biomarkers are required. Biomarkers used in cancer range from macromolecules, such as DNA, RNA, and proteins, to whole cells. Biomarkers for cancer risk, diagnosis, proliferation, metastasis, drug resistance, and prognosis have been identified in breast cancer. In addition, there is currently a greater demand for personalized or precise treatments; moreover, the identification of novel biomarkers to further the development of new drugs is urgently needed. In this review, we summarize and focus on the recent discoveries of promising macromolecules and cell-based biomarkers for the diagnosis and prognosis of breast cancer and provide implications for therapeutic strategies.

Clinical Challenges in the Management of Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer: A Literature Review

Endocrine therapy (ET) is integral to the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2−) metastatic breast cancer (MBC). Aromatase inhibitors (AIs; e.g., anastrozole, letrozole, exemestane), selective estrogen receptor modulators (e.g., tamoxifen), and the selective estrogen receptor degrader, fulvestrant, inhibit tumor cell proliferation by targeting ER signaling. However, the efficacy of ET could be limited by intrinsic and acquired resistance mechanisms, which has prompted the development of targeted agents and combination strategies. In recent years, the treatment landscape for HR+, HER2− MBC has evolved rapidly. AIs, historically the first-line treatment for postmenopausal patients with HR+, HER2− MBC, have been challenged by more effective ET, such as fulvestrant alone or in combination with an AI, and the cyclin-dependent kinase (CDK)4/6 inhibitors, which have increasingly become the new standard of care. For endocrine-resistant disease (≥ second-line), clinical trials demonstrated that the mammalian target of rapamycin inhibitor, everolimus, enhanced the efficacy of exemestane or fulvestrant after progression on an AI. CDK4/6 inhibitors in combination with fulvestrant have demonstrated superior progression-free survival and overall survival versus fulvestrant alone. Recently, the combination of fulvestrant with alpelisib in phosphatidylinositol-4,5-bisphosphate 3-kinase (PIK3CA) mutated HR+, HER2− MBC following progression on or after ET was approved, based on the SOLAR-1 study. However, the optimal sequencing of treatments is unknown, especially following disease progression on a CDK4/6 inhibitor. This review aims to provide practical guidance for the management of HR+, HER2− MBC based on available data and the utility of genomic biomarkers, including germline breast cancer genes 1 and 2 (BRCA1/2) mutations, and somatic estrogen receptor alpha gene (ESR1), HER2, and PIK3CA mutations.

Navitoclax combined with Alpelisib effectively inhibits Merkel cell carcinoma cell growth in vitro

Background:

Merkel cell carcinoma (MCC) is a highly malignant skin cancer. Despite major treatment improvements during the last decade, up to 50% of patients do not respond to therapy or develop recurrent disease. For these patients, alternative treatment options are urgently needed. Here, we assessed the efficacy of the combination of the BCL-2 inhibitor Navitoclax and the PI3K p110α inhibitor Alpelisib in MCC cell lines.

Methods:

The expression of BCL-2 was assessed by immunohistochemistry in MCC and MCC cell lines. Treatment with Navitoclax and Alpelisib alone and in combination was performed on four MCC cell lines. The decrease of cell viability during treatment was assessed by XTT assay and visualized for the combinations by 3D combinatorial index plotting. The increase of apoptotic cells was determined by cleaved PARP Western blotting and Annexin V staining.

Results:

Some 94% of MCCs and all three MCPyV-positive cell lines showed BCL-2 expression. Navitoclax monotreatment was shown to be highly effective when treating BCL-2-positive cell lines (IC₅₀-values ranging from 96.0 to 323.0 nM). The combination of Alpelisib and Navitoclax resulted in even stronger synergistic and prolonged inhibitions of MCC cell viability through apoptosis up to 4 days.

Discussion:

Our results show that the anti-apoptotic BCL-2 is frequently expressed in MCC and MCC cell lines. Inhibition of BCL-2 by Navitoclax in combination with Alpelisib revealed a strong synergy and prolonged inhibition of MCC cell viability and induction of apoptosis. The combination of Navitoclax and Alpelisib is a novel potential treatment option for MCC patients.

Sequencing for an interdisciplinary molecular tumor board in patients with advanced breast cancer: experiences from a case series

Purpose: High throughput panel sequencing to tailor therapy in precision oncology promises to improve outcome in patients with metastatic breast cancer. However, data that clearly show any benefit from such an approach is still pending.

Materials and Methods: We performed a retrospective analysis of advanced breast cancer patients that underwent panel sequencing for suggestion of target related drugs. We aimed to (i) determine the frequency of actionable mutations per patient and to (ii) assess the clinical impact of results on treatment options.

Results: A total of 52 patients underwent panel sequencing of archived tumor tissue. Every sample showed at least one affected gene, accounting for actionable mutations in 45 of 52 patients (87%). New treatment options that would not have been used as indicated by standard predictive markers (such as hormonal receptor status or HER2-status) were found in 22 of 52 patients (42%). We detected therapeutic relevant pathogenic germline variants in 9,6% (5/52) of the patients.

Conclusions: Using a high throughput-panel sequencing approach to identify actionable mutations in patients with metastatic breast cancer, we identified potential target-related treatment options in a large proportion of our patients, some of which would not have been considered without this data. Prospective clinical trials with compounds targeting the identified actionable mutations are needed to determine which treatments can indeed improve survival or quality of life by limiting exposure to ineffective drugs in advanced breast cancer.

Endocrine therapy-based treatments in hormone receptor-positive/HER2-negative advanced breast cancer: systematic review and network meta-analysis

BACKGROUND

Several endocrine therapy (ET)-based treatments are available for patients with advanced breast cancer. We assessed the efficacy of different ET-based treatments in patients with hormone receptor-positive/HER2-negative advanced breast cancer with endocrine-sensitive or endocrine-resistant disease.

METHODS

We searched Medline and Cochrane Central Register of Controlled Trials up to 15 October 2019 and abstracts from major conferences from 2016 to October 2019. We included phase II/III randomised trials, comparing ≥2 ET-based treatments. Progression-free survival (PFS) and overall survival (OS) were analysed by network meta-analyses using MTC Bayesian models based on both fixed-effect and random-effect models; relative treatment effects were measured as HRs and 95% credibility intervals (CrI). All statistical tests were two-sided. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed and this systematic review is registered in the PROSPERO database.

RESULTS

55 publications reporting on 32 trials (n=12 293 patients) were included. Regarding PFS in the endocrine sensitive setting (n=5200; 12 trials), the combination of cyclin-dependent kinases (CDK)4/6-inhibitors (CDK4/6i)+fulvestrant 500 mg (F500) was likely the most effective treatment (surface under the cumulative ranking curve (SUCRA)=97.3%), followed by CDK4/6i+aromatase inhibitor ±goserelin; there was no significant difference between them (HR 0.82; 95% CrI 0.54-1.25). Regarding OS (n=2157; five trials), the most effective treatment was probably CDK4/6i+F500 (SUCRA=97.3%); comparing CDK4/6i+F500 versus F500 held a HR of 0.77 (95% CrI 0.63-0.95). Regarding PFS in the endocrine-resistant setting (n=6635; 20 trials), CDK4/6i+F500 was likely the most effective treatment (SUCRA=95.7%), followed by capivasertib+F500, without significant difference between them (HR 0.91; 95% CrI 0.60-1.36). For OS (n=4377; 11 trials), the most effective treatments were capivasertib+F500 (SUCRA=84.7%) and CDK4/6i+F500 (SUCRA=69.9%). Comparing CDK4/6i+F500 versus F500 held a HR of 0.77 (95% CrI 0.67-0.89).

CONCLUSIONS

CDK4/6i+F500 is likely the best treatment option in both endocrine-sensitive and endocrine-resistant diseases for PFS, and in endocrine-sensitive patients for OS. Concerning OS in endocrine-resistant patients, capivasertib+F500 and CDK4/6i+F500 are likely the best treatments.

PROSPERO REGISTRATION NUMBER

CRD42018104628.

Performance of a novel Next Generation Sequencing circulating tumor DNA (ctDNA) platform for the evaluation of samples from patients with metastatic breast cancer (MBC)

Circulating tumor DNA (ctDNA) is gaining momentum as sensitive diagnostic tool for advanced disease characterization because of its ability both to capture the tumor's heterogeneity and its dynamic adaptations. However, the consistency between all the available platforms is still debated. The aim of the study was to explore the performance of the novel diagnostic NGS platform PredicinePLUS™ and to compare its results with the clinically available Guardant360™ platform for possible analytical inconsistencies. The study suggests that PredicinePLUS™ NGS platform can detect genomic alterations and measure allele frequency in samples of MBC patients and confirmed that different NGS platforms could be potentially compared provided that certain sample management and analytical requirements are met.

Targeting Apoptosis: A New Paradigm for the Treatment of Estrogen Receptor-Positive Breast Cancer

Standard treatment for estrogen receptor-positive metastatic breast cancer involves antiestrogen therapy used alone or in combination with inhibitors of CDK4/6 or mTOR; this approach works mechanistically by eliciting and reinforcing cell-cycle arrest. In this issue, Lok and colleagues diverge from this paradigm by combining the BCL2 inhibitor venetoclax with tamoxifen in a phase Ib clinical trial, building on preclinical work to demonstrate that targeting apoptosis could represent a promising new strategy in the treatment of breast cancer.See related article by Lok et al., p. 354.

The Novel Phosphatidylinositol-3-Kinase (PI3K) Inhibitor Alpelisib Effectively Inhibits Growth of PTEN-Haploinsufficient Lipoma Cells

Germline mutations in the tumor suppressor gene PTEN cause PTEN Hamartoma Tumor Syndrome (PHTS). Pediatric patients with PHTS frequently develop lipomas. Treatment attempts with the mTORC1 inhibitor rapamycin were unable to reverse lipoma growth. Recently, lipomas associated with PIK3CA-related overgrowth syndrome were successfully treated with the novel PI3K inhibitor alpelisib. Here, we tested whether alpelisib has growth-restrictive effects and induces cell death in lipoma cells. We used PTEN-haploinsufficient lipoma cells from three patients and treated them with alpelisib alone or in combination with rapamycin. We tested the effect of alpelisib on viability, proliferation, cell death, induction of senescence, adipocyte differentiation, and signaling at 1-100 µM alpelisib. Alpelisib alone or in combination with rapamycin reduced proliferation in a concentration- and time-dependent manner. No cell death but an induction of senescence was detected after alpelisib incubation for 72 h. Alpelisib treatment led to a reduced phosphorylation of AKT, mTOR, and ribosomal protein S6. Rapamycin treatment alone led to increased AKT phosphorylation. This effect could be reversed by combining rapamycin with alpelisib. Alpelisib reduced the size of lipoma spheroids by attenuating adipocyte differentiation. Since alpelisib was well tolerated in first clinical trials, this drug alone or in combination with rapamycin is a potential new treatment option for PHTS-related adipose tissue overgrowth.

Available and emerging molecular markers in the clinical management of breast cancer

Introduction: Biomarker assessment is fundamental to managing patients with invasive breast cancer. While the assessment of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 is mandatory for all invasive breast tumors, recent advances in our understanding of tumor biology have uncovered a growing list of clinically relevant biomarkers. Areas covered: In early-stage breast cancer, we focus on dynamic changes in Ki-67 during neoadjuvant endocrine therapy and multigene prognostic assays to guide adjuvant chemotherapy decisions. In advanced breast cancer, we discuss the techniques and clinical relevance of ESR1 and PIK3CA mutations in cell-free DNA and describe therapeutically targetable germline or somatic alterations, with specific focus on BRCA mutations, microsatellite instability, and NTRK fusions. Expert opinion: Biomarkers influence breast cancer management at every stage of disease. This review summarizes recently identified tissue and blood-based biomarkers, implications on clinical management, current limitations and future developments in both early- and advanced-stage breast cancer.

Breast cancer

Breast cancer is the most frequent malignancy in women worldwide and is curable in ~70-80% of patients with early-stage, non-metastatic disease. Advanced breast cancer with distant organ metastases is considered incurable with currently available therapies. On the molecular level, breast cancer is a heterogeneous disease; molecular features include activation of human epidermal growth factor receptor 2 (HER2, encoded by ERBB2), activation of hormone receptors (oestrogen receptor and progesterone receptor) and/or BRCA mutations. Treatment strategies differ according to molecular subtype. Management of breast cancer is multidisciplinary; it includes locoregional (surgery and radiation therapy) and systemic therapy approaches. Systemic therapies include endocrine therapy for hormone receptor-positive disease, chemotherapy, anti-HER2 therapy for HER2-positive disease, bone stabilizing agents, poly(ADP-ribose) polymerase inhibitors for BRCA mutation carriers and, quite recently, immunotherapy. Future therapeutic concepts in breast cancer aim at individualization of therapy as well as at treatment de-escalation and escalation based on tumour biology and early therapy response. Next to further treatment innovations, equal worldwide access to therapeutic advances remains the global challenge in breast cancer care for the future.

Advances in Targeted Therapies for Triple-Negative Breast Cancer

While the outcomes for patients diagnosed with hormone receptor positive (HR+) and/or human epidermal growth factor receptor 2-positive (HER2+) breast cancers have continued to improve with the development of targeted therapies, the same cannot be said yet for those affected with triple-negative breast cancer (TNBC). Currently, the mainstay of treatment for the 10-15% of patients diagnosed with TNBC remains cytotoxic chemotherapy, but it is hoped that through an enhanced characterization of TNBC biology, this disease will be molecularly delineated into subgroups with targetable oncogenic drivers. This review will focus on recent therapeutic innovations for TNBC, including poly-ADP-ribosyl polymerase (PARP) inhibitors, phosphoinositide 3-kinase (PI3K) pathway inhibitors, immune checkpoint inhibitors, and cyclin-dependent kinase (CDK) inhibitors.

Neoadjuvant letrozole plus taselisib versus letrozole plus placebo in postmenopausal women with oestrogen receptor-positive, HER2-negative, early-stage breast cancer (LORELEI): a multicentre, randomised, double-blind, placebo-controlled, phase 2 trial

BACKGROUND

Endocrine therapy-based neoadjuvant treatment for luminal breast cancer allows efficient testing of new combinations before surgery. The activation of the phosphatidylinositol-3-kinase (PI3K) pathway is a known mechanism of resistance to endocrine therapy. Taselisib is an oral, selective PI3K inhibitor with enhanced activity against PIK3CA-mutant cancer cells. The LORELEI trial tested whether taselisib in combination with letrozole would result in an increased proportion of objective responses and pathological complete responses.

METHODS

In this multicentre, randomised, double-blind, parallel-cohort, placebo-controlled phase 2, study, we enrolled postmenopausal women (aged ≥18 years) with histologically confirmed, oestrogen receptor (ER)-positive, HER2-negative, stage I-III, operable breast cancer, from 85 hospitals in 22 countries worldwide. To be eligible, patients had have an Eastern Cooperative Oncology Group (ECOG) performance status 0-1, adequate organ function, and had to have evaluable tumour tissue for PIK3CA genotyping. Patients were randomly assigned (1:1) by means of a permuted block algorithm (block size of four) via an interactive voice or web-based response system, to receive letrozole (2·5 mg/day orally, continuously) with either 4 mg of oral taselisib or placebo (on a 5 days-on, 2 days-off schedule) for 16 weeks, followed by surgery. Randomisation was stratified by tumour size and nodal status. Site staff, patients, and the sponsor were masked to treatment assignment. Coprimary endpoints were the proportion of patients who achieved an objective response by centrally assessed breast MRI and a locally assessed pathological complete response in the breast and axilla (ypT0/Tis, ypN0) at surgery in all randomly assigned patients and in patients with PIK3CA-mutant tumours. Analyses were done in the intention-to-treat population. This trial is registered with ClinicalTrials.gov, number NCT02273973, and is closed to accrual.

FINDINGS

Between Nov 12, 2014, and Aug 12, 2016, 334 participants were enrolled and randomly assigned to receive letrozole and placebo (n=168) or letrozole and taselisib (n=166). Median follow-up was 4·9 months (IQR 4·7-5·1). The study met one of its primary endpoints: the addition of taselisib to letrozole was associated with a higher proportion of patients achieving an objective response in all randomly assigned patients (66 [39%] of 168 patients in the placebo group vs 83 [50%] of 166 in the taselisib group; odds ratio [OR] 1·55, 95% CI 1·00-2·38; p=0·049) and in the PIK3CA-mutant subset (30 [38%] of 79 vs 41 [56%] of 73; OR 2·03, 95% CI 1·06-3·88; p=0·033). No significant differences were observed in pathological complete response between the two groups, either in the overall population (three [2%] of 166 in the taselisib group vs one [1%] of 168 in the placebo group; OR 3·07 [95% CI 0·32-29·85], p=0·37) or in the PIK3CA-mutant cohort (one patient [1%) vs none [0%]; OR not estimable, p=0·48). The most common grade 3-4 adverse events in the taselisib group were gastrointestinal (13 [8%] of 167 patients), infections (eight [5%]), and skin-subcutaneous tissue disorders (eight [5%]). In the placebo group, four (2%) of 167 patients had grade 3 or worse vascular disorders, two (1%) had gastrointestinal disorders, and two (1%) patients had grade 3 or worse infections and infestations. There was no grade 4 hyperglycaemia and grade 3 cases were asymptomatic. Serious adverse events were more common in the taselisib group (eight [5%] patients with infections and seven [4%] with gastrointestinal effects) than in the placebo group (one [1%] patient each with grade 3 postoperative wound and haematoma infection, grade 4 hypertensive encephalopathy, grade 3 acute cardiac failure, and grade 3 breast pain). One death occurred in the taselisib group, which was not considered to be treatment-related.

INTERPRETATION

The increase in the proportion of patients who achieved an objective response from the addition of taselisib to endocrine therapy in a neoadjuvant setting is consistent with the clinical benefit observed in hormone receptor-positive, HER2-negative, metastatic breast cancer.

FUNDING

Genentech and F Hoffmann-La Roche.

ESR1 mutations in breast cancer

The acquisition of ligand-independent ESR1 mutations during aromatase inhibitor therapy in metastatic estrogen receptor (ER)-positive breast cancer is a common mechanism of hormonal therapy resistance. Preclinical and clinical studies have demonstrated that ESR1 mutations can preexist in primary tumors and can be enriched during metastasis. Furthermore, ESR1 mutations express a unique transcriptional profile that favors tumor progression, suggesting that selected ESR1 mutations may influence metastasis. Several groups have used sensitive detection methods using patient liquid biopsies to track ESR1 or truncal somatic mutations to predict treatment outcome and tumor progression, and some of these techniques may eventually be used to guide sequential treatment options in patients. Further development and standardization of mutation tracking in circulating tumor DNA is ongoing. Clinically, patients with ESR1 mutations derive clinical benefit when treated with fulvestrant and CDK4/6-targeted therapies, but the development of more potent selective ER degraders and/or new targeted biotherapies are needed to overcome the endocrine-resistant phenotype of ESR1 mutant-bearing tumors. In this review, we discuss the mechanisms of resistance and dissemination of ESR1 mutations as well as the detection methods for ESR1 mutation tracking, newly discovered potential therapeutic targets, and the clinical implications and treatment options for treating patients with ESR1 mutant-bearing tumors.

Safety and Tolerability of Phosphatidylinositol-3-Kinase (PI3K) Inhibitors in Oncology

Activation of phosphatidylinositol-3-kinase (PI3K) and downstream signalling by AKT/mammalian target of rapamycin (mTOR) modulates cellular processes such as increased cell growth, cell proliferation and increased cell migration as well as deregulated apoptosis and oncogenesis. The PI3K/AKT/mTOR pathway (particularly Class I PI3K isoforms) is frequently activated in a variety of solid tumours and haematological malignancies, making PI3K an attractive therapeutic target in oncology. Inhibitors of PI3K also have the potential to restore sensitivity to other modalities of treatments when administered as part of combination regimens. Although many PI3K inhibitors have reached different stages of clinical development, only two (idelalisib and copanlisib) have been currently approved for use in the treatment of B cell lymphoma and leukaemias. While these two agents are effective clinically, their use is associated with a number of serious class-related as well as drug-specific adverse effects. Some of these are immune-mediated and include cutaneous reactions, severe diarrhoea with or without colitis, hepatotoxicity and pneumonitis. They also induce various metabolic abnormalities such as hyperglycaemia and hypertriglyceridaemia. Not surprisingly, therefore, many new PI3K inhibitors with a varying degree of target selectivity have been synthesised in expectations of improved safety and efficacy, and are currently under clinical investigations for use in a variety of solid tumours as well as haematological malignancies. However, evidence from early clinical trials, reviewed herein, suggests that these newer agents are also associated not only with class-related but also other serious and unexpected adverse effects. Their risk/benefit evaluations have resulted in a number of them being discontinued from further development. Cumulative experience with the use of PI3K inhibitors under development suggests that, compared with their use as monotherapy, combining them with other anticancer therapies may be a more effective strategy in improving current standard-of-care and clinical outcomes in cancers beyond haematological cancers. For example, combination of alpelisib with fulvestrant has recently demonstrated unexpectedly superior efficacy compared to fulvestrant alone. Furthermore, the immunomodulatory activity of PI3Kδ and PI3Kγ inhibitors also provides unexpected opportunities for their use in cancer immunotherapy, as is currently being tested in several clinical trials.

Endocrine and Targeted Therapy for Hormone-Receptor-Positive, HER2-Negative Advanced Breast Cancer: Insights to Sequencing Treatment and Overcoming Resistance Based on Clinical Trials

Background: Advanced hormone-receptor positive HER2 negative breast cancer is a common and a very heterogeneous disease. Hormone therapy is the main first line treatment of choice, given alone or in combination with other agents that have shown to improve patient outcomes, Nevertheless, treatment remains generally palliative rather than curative. Sequencing of such treatment remains challenging, especially with resurgence of variable resistance patterns. Multiple attempts have been made to overcome resistance and improve patient survival, yet resistance remains not very well understood and metastatic cancer remains a disease with dismal prognosis.

Methods: In this paper, we searched pubmed database as well as local and international meetings for all studies discussing advanced and metastatic hormone-receptor-positive, her2-negative breast cancer, hormonal treatment, resistance to hormonal treatment, mechanism of resistance, and means to overcome such resistance.

Conclusion: There does not exist an optimal treatment sequence for hormone-receptor-positive, her2-negative advanced breast cancer. However, after review of literature, a reasonable approach may be starting with tamoxifen, aromatase inhibitors, or fulvestrant in absence of visceral crisis, in addition to ensuring adequate ovarian function suppression in pre/peri-menopausal women. Aromatase inhibitors and fulvestrant seem to be superior. Resistance to such agents is increasing, mostly attributed to genetic and molecular changes. Multiple modalities are addressed to overcome such resistance including use of CKD4/6 inhibitors, mTOR inhibitors and PI3K inhibitors in addition to other agents under study, all with promising results. CDK4/6 inhibitors work best when used in frontline setting. Finally, treatment of breast cancer remains a growing field, and more studies are to be awaited.

Phase I study of BGT226, a pan-PI3K and mTOR inhibitor, in Japanese patients with advanced solid cancers

The phosphatidylinositol 3-kinase (PI3K) pathway is a promising therapeutic target for various cancers. BGT226 is a pan-PI3K and mammalian target of rapamycin (mTOR) inhibitor. The tolerability and pharmacokinetics/pharmacodynamics of BGT226 were investigated in a phase I study in Japanese patients with advanced solid cancers. BGT226 was orally administered on days 1, 3, and 5 of each week. The initial dose of 10 mg was subsequently escalated to 20, 40, 80, and 100 mg in a cohort of three patients. Pharmacokinetics and pharmacodynamics were investigated using plasma, normal skin, and tumor samples. A total of 18 patients were enrolled and evaluated. The most frequently reported toxicities were diarrhea, nausea, decreased appetite, vomiting, and fatigue. They were all grade 1 or 2, and no dose-limiting toxicity was observed. However, all six patients treated at 100 mg experienced diarrhea and nausea, while two experienced a dose reduction and/or interruptions during the study. Two of five patients who exhibited stable disease continued the study treatment for ≥ 16 weeks. The absorption of BGT226 was rapid, and systemic exposure increased in a dose-dependent manner. Treatment with BGT226 did not change any of the biomarkers in neither normal skin nor tumor tissues. BGT226 was tolerated up to 100 mg three times a week in Japanese patients with solid cancers, without difference in toxicity profiles and pharmacokinetics compared to Western patients.

PI3Kα inhibitors sensitize esophageal squamous cell carcinoma to radiation by abrogating survival signals in tumor cells and tumor microenvironment

Radiotherapy is one of the standard therapies for esophageal squamous cell carcinoma (ESCC), but the efficacy is far from desirable. Large scale genome sequencing reveals PI3Kα is frequently hyper-activated in ESCC. We found that ESCC cells harboring alterations in PI3K pathway were more resistant to radiation and combination of a clinical PI3Kα-selective inhibitor CYH33 and radiation synergistically inhibited cell proliferation in 14 ESCC cell lines. Radiation induced phosphorylation of FOXO1 and Akt, which sensitized ESCC cells to PI3Kα inhibitors. Both S1PR3 and DNA-PK contributed to radiation-induced Akt phosphorylation, which were revealed to be collectively dependent on PI3Kα. By contrast, constitutively active Akt abrogated the synergism between PI3Kα inhibitors and radiation. PI3Kα inhibition enhanced radiation-induced DNA damage, G2/M arrest and apoptosis. Combination of CYH33 and radiation significantly inhibited the growth of xenografts derived from ESCC patients, which was accompanied with abrogation of radiation-induced phosphorylation of Akt and filtration of M2-like macrophages. Taken together, combination of CYH33 and radiation possesses synergism in ESCC, which provides promising rationale to test this combinatorial regimen in ESCC patients.

Molecular Testing in Breast Cancer

Molecular testing for genetic and genomic variation has become an integral part of breast cancer management. Patients with a family history of breast cancer or other tumors, bilateral breast cancers, or early-onset breast cancers warrant genetic testing to determine whether a hereditary cancer syndrome is present. The availability of PARP inhibitors-drugs that are selectively active in BRCA1/2-associated breast cancers-has created the need for hereditary cancer testing for all patients diagnosed with advanced breast cancer. Tumor genomic profiling is the standard of care for many types of malignancies and is becoming increasingly important in the management of advanced breast cancer. Targetable mutations in advanced breast cancer include PIK3CA, HER2, and rare instances of mismatch deficiency or other targets for tyrosine kinase inhibitors. The development of methods for sequencing cell-free DNA should allow for broader and easier implementation of tumor genomic testing. Transcriptome-based expression signatures have become the standard of care in the management of early-stage estrogen receptor-positive breast cancers. These assays provide prognostic significance in the setting of adjuvant endocrine therapy and are predictive for benefit from adjuvant chemotherapy. Collectively, these developments underscore the contemporary reality that molecular testing is now part of the clinical management for the majority of patients with breast cancer.

A Phase II Randomized Study of Neoadjuvant Letrozole Plus Alpelisib for Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer (NEO-ORB)

PURPOSE

Addition of alpelisib to fulvestrant significantly extended progression-free survival in PIK3CA-mutant, hormone receptor-positive (HR+) advanced/metastatic breast cancer in the phase III SOLAR-1 study. The combination of alpelisib and letrozole also had promising activity in phase I studies of HR+ advanced/metastatic breast cancer. NEO-ORB aimed to determine whether addition of alpelisib to letrozole could increase response rates in the neoadjuvant setting.Patients and Methods: Postmenopausal women with HR+, human epidermal growth factor receptor 2-negative, T1c-T3 breast cancer were assigned to the PIK3CA-wild-type or PIK3CA-mutant cohort according to their tumor PIK3CA status, and randomized (1:1) to 2.5 mg/day letrozole with 300 mg/day alpelisib or placebo for 24 weeks. Primary endpoints were objective response rate (ORR) and pathologic complete response (pCR) rate for both PIK3CA cohorts.

RESULTS

In total, 257 patients were assigned to letrozole plus alpelisib (131 patients) or placebo (126 patients). Grade ≥3 adverse events (≥5% of patients) in the alpelisib arm were hyperglycemia (27%), rash (12%), and maculo-papular rash (8%). The primary objective was not met; ORR in the alpelisib versus placebo arm was 43% versus 45% and 63% versus 61% in the PIK3CA-mutant and wild-type cohorts, respectively. pCR rates were low in all groups. Decreases in Ki-67 were similar across treatment arms and cohorts. In PIK3CA-mutant tumors, alpelisib plus letrozole treatment induced a greater decrease in phosphorylated AKT versus placebo plus letrozole.

CONCLUSIONS

In contrast to initial results in advanced/metastatic disease, addition of alpelisib to 24-week neoadjuvant letrozole treatment did not improve response in patients with HR+ early breast cancer.

Treating cancer with phosphatidylinositol-3-kinase inhibitors: increasing efficacy and overcoming resistance

The discovery of the phosphatidylinositol-3-kinase (PI3K) pathway was a major advance in understanding growth factor signaling. The high frequency of PI3K pathway mutations in many cancers has encouraged a new field targeting cancer driver mutations. Although there have been many successes, targeting PI3K itself has proven challenging, in part because of its multiple isoforms with distinct roles. Despite promising preclinical results, development of PI3K inhibitors as pharmacologic anticancer agents has been limited by modest single-agent efficacy and significant adverse effects. If we could overcome these limitations, PI3K inhibitors would be a powerful cancer-fighting tool. Data from phase III clinical trials yields insight into some of the problems with PI3K inhibitors. Recent advances have shed light on the mechanisms of tumor resistance to PI3K inhibitors via feedback pathways that cause elevated insulin levels that then activate the same PI3K pathways that are the targets of inhibition. Improving our understanding of the complex regulatory feedback pathways that activate in response to PI3K inhibition will reveal ways to increase the efficacy of PI3K inhibitors and reduce adverse effects, increasing the usefulness of this class as a treatment option for multiple cancer types.

Challenges for the Clinical Development of PI3K Inhibitors: Strategies to Improve Their Impact in Solid Tumors

The PI3K pathway is mutated and aberrantly activated in many cancers and plays a central role in tumor cell proliferation and survival, making it a rational therapeutic target. Until recently, however, results from clinical trials with PI3K inhibitors in solid tumors have been largely disappointing. Here, we describe several factors that have limited the success of these agents, including the weak driver oncogenic activity of mutant PI3K, suboptimal patient selection in trials, drug-related toxicities, feedback upregulation of compensatory mechanisms when PI3K is blocked, increased insulin production upon PI3Kα inhibition, lack of mutant-specific inhibitors, and a relative scarcity of studies using combinations with PI3K antagonists. We also suggest strategies to improve the impact of these agents in solid tumors. Despite these challenges, we are optimistic that isoform-specific PI3K inhibitors, particularly in combination with other agents, may be valuable in treating appropriately selected patients with PI3K-dependent tumors. SIGNIFICANCE: Despite the modest clinical activity of PI3K inhibitors in solid tumors, there is an increasing understanding of the factors that may have limited their success. Strategies to ameliorate drug-related toxicities, use of rational combinations with PI3K antagonists, development of mutant-selective PI3K inhibitors, and better patient selection should improve the success of these targeted agents against solid tumors.

Circulating tumor DNA analysis in breast cancer: Is it ready for prime-time?

Precision Medicine is becoming the new paradigm in healthcare as it enables better resources allocation, treatment optimization with a potential side-effects reduction and consequent impact on quality of life and survival. This revolution is being catalyzed by liquid biopsy technologies, which provide prognostic and predictive information for advanced cancer patients, without the analytical and procedural drawbacks of tissue-biopsy. In particular, circulating tumor DNA (ctDNA) is gaining momentum as a clinically feasible option capable to capture both spatial and temporal tumor heterogeneity. Several techniques are currently available for ctDNA extraction and analysis, each with its preferential case scenarios and preanalytical implications which must be taken into consideration to effectively support clinical decision-making and to better highlight its clinical utility. Aim of this review is to summarize both analytical developments and clinical evidences to offer a comprehensive update on the deployment of ctDNA in breast cancer's (BC) characterization and treatment.