Recent progress of CDK4/6 inhibitors' current practice in breast cancer

Dysregulated cellular proliferation represents a hallmark feature across all cancers. Aberrant activation of the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway, independent of mitogenic signaling, engenders uncontrolled breast cancer cell proliferation. Consequently, the advent of CDK4/6 inhibition has constituted a pivotal milestone in the realm of targeted breast cancer therapy. The combination of CDK4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) has emerged as the foremost therapeutic modality for patients afflicted with hormone receptor-positive (HR + )/HER2-negative (HER2-) advanced breast cancer. At present, the Food and Drug Administration (FDA) has sanctioned various CDK4/6i for employment as the primary treatment regimen in HR + /HER2- breast cancer. This therapeutic approach has demonstrated a substantial extension of progression-free survival (PFS), often amounting to several months, when administered alongside endocrine therapy. Within this comprehensive review, we systematically evaluate the utilization strategies of CDK4/6i across various subpopulations of breast cancer and explore potential therapeutic avenues following disease progression during application of CDK4/6i therapy.

Phase Ia/b Study of Giredestrant ± Palbociclib and ± Luteinizing Hormone-Releasing Hormone Agonists in Estrogen Receptor-Positive, HER2-Negative, Locally Advanced/Metastatic Breast Cancer

PURPOSE

Giredestrant is an investigational next-generation, oral, selective estrogen receptor antagonist and degrader for the treatment of estrogen receptor-positive (ER+) breast cancer. We present the primary analysis results of the phase Ia/b GO39932 study (NCT03332797).

PATIENTS AND METHODS

Patients with ER+, HER2-negative locally advanced/metastatic breast cancer previously treated with endocrine therapy received single-agent giredestrant (10, 30, 90, or 250 mg), or giredestrant (100 mg) ± palbociclib 125 mg ± luteinizing hormone-releasing hormone (LHRH) agonist. Detailed cardiovascular assessment was conducted with giredestrant 100 mg. Endpoints included safety (primary), pharmacokinetics, pharmacodynamics, and efficacy.

RESULTS

As of January 28, 2021, with 175 patients enrolled, no dose-limiting toxicity was observed, and the MTD was not reached. Adverse events (AE) related to giredestrant occurred in 64.9% and 59.4% of patients in the single-agent ± LHRH agonist and giredestrant + palbociclib ± LHRH agonist cohorts, respectively (giredestrant-only-related grade 3/4 AEs were reported in 4.5% of patients across the single-agent cohorts and 3.1% of those with giredestrant + palbociclib). Dose-dependent asymptomatic bradycardia was observed, but no clinically significant changes in cardiac-related outcomes: heart rate, blood pressure, or exercise duration. Clinical benefit was observed in all cohorts (48.6% of patients in the single-agent cohort and 81.3% in the giredestrant + palbociclib ± LHRH agonist cohort), with no clear dose relationship, including in patients with ESR1-mutated tumors.

CONCLUSIONS

Giredestrant was well tolerated and clinically active in patients who progressed on prior endocrine therapy. Results warrant further evaluation of giredestrant in randomized trials in early- and late-stage ER+ breast cancer.

Comparative overall survival of CDK4/6 inhibitors in combination with endocrine therapy in advanced breast cancer

Individual trials of abemaciclib, palbociclib, and ribociclib show a similar impact on progression-free survival yet differing statistical significance for overall survival (OS). A robust comparative evaluation of OS, safety, and tolerability of the three drugs is warranted. A systematic literature search identified phase 3 randomized clinical trials reporting OS of CDK4/6 inhibitors (CDK4/6i) in combination with endocrine therapy in ER-positive/HER2-negative advanced breast cancer. Trial-level data on OS and common and serious adverse events (AE) were extracted for each drug. In the absence of direct comparisons, a network meta-analysis was performed to evaluate pairwise comparative efficacy, safety, and tolerability of each of the CDK4/6i. Seven studies comprising of 4415 patients met the inclusion criteria. Median follow-up was 73.3 months (range: 48.7-97.2 months). There were no statistically significant differences in OS between any of the CDK4/6i. Compared to palbociclib, ribociclib and abemaciclib both showed significantly higher GI toxicity (grade 1-2 vomiting OR 1.87 [95% CI 1.37-2.56] and OR 2.27 [95% CI 1.59-3.23] respectively). Compared to palbociclib, abemaciclib was associated with more grade 3-4 diarrhea OR 118.06 [95% CI 7.28-1915.32]. In contrast, palbociclib was associated with significantly more neutropenia than ribociclib and abemaciclib but significantly lower risk of grade 3-4 infections. Abemaciclib had significantly less grade 3-4 transaminitis and grade 3-4 neutropenia than ribociclib. Treatment discontinuation and death due to AE were significantly higher with abemaciclib than palbociclib and ribociclib. There is no statistically significant difference in OS between CDK4/6i despite differing statistical significance levels of individual trials. Real-world data analyses may help to identify if there is a meaningful inter-drug difference in efficacy. Significant differences between CDK4/6i are observed for safety and tolerability outcomes.

Cardiac Interventions in Patients With Active, Advanced Solid and Hematologic Malignancies: JACC: CardioOncology State-of-the-Art Review

Invasive cardiac interventions are recommended to treat ST-segment elevation myocardial infarction, non-ST-segment elevation acute coronary syndromes, multivessel coronary disease, severe symptomatic aortic stenosis, and cardiomyopathy. These recommendations are based on randomized controlled trials that historically included few individuals with active, advanced malignancies. Advanced malignancies represent a significant competing risk for mortality, and there is limited evidence to inform the risks and benefits of invasive cardiac interventions in affected patients. We review the benefit conferred by invasive cardiac interventions; the periprocedural considerations; the contemporary survival expectations of patients across several types of active, advanced malignancy; and the literature on cardiovascular interventions in these populations. Our objective is to develop a rational framework to guide clinical recommendations on the use of invasive cardiac interventions in patients with active, advanced cancer.

Real-World Outcomes of CDK4/6 Inhibitors Treatment in Metastatic Breast Cancer in Romania

The introduction in clinical practice of selective cyclin-dependent kinase (CDK) 4/6 inhibitors improves the outcome of patients with hormone receptor (HR)-positive human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (mBC). In Romania, the three available CDK 4/6 inhibitors (Palbociclib, Ribociclib and Ademaciclib) have been approved by the National Agency for Medicines (ANM) in 2019, 2020 and 2021. We conducted a retrospective study from 2019 to 2022 on 107 patients with metastatic breast cancer HR+ that have been treated with CDK 4/6 inhibitors in addition to hormone therapy in the Oncology Department of Colțea Clinical Hospital in Bucharest. The purpose of this study is to calculate the median progression-free survival (PFS) and to compare it with the median PFS from other randomized clinical trials. A key difference from other studies is that our study evaluated both patients with non-visceral mBC and patients with visceral mBC, as these two groups often have different outcomes. A total of 79.4% were postmenopausal patients and 20.6% were premenopausal; 42.1% had different stages at the beginning of disease and 57.9% presented newly metastatic disease. Median PFS was 17 months, unlike randomized clinical trials which reported a median PFS of 25.3 months. The combination of CDK 4/6 inhibitors with endocrine therapy is the golden standard treatment in HR-positive, HER2-negative metastatic breast cancer, bringing a prolongation of survival for these patients. Our results show no major differences compared to randomized clinical trials, despite the smaller patient group. In order to have a picture of the efficacy of the treatment as close as possible to the real-world data, we believe that it would be very useful to have a collaboration between several oncology departments in different institutions to carry out a multi-center study on large groups of patients.

How I treat endocrine-dependent metastatic breast cancer

Estrogen receptor-positive (ER+)/HER2-negative (HER2-), the so-called luminal-type breast cancer, is the most frequent subset, accounting for around 70% of all breast cancer cases. Endocrine therapy (ET) combined with cyclin-dependent kinases (CDK) 4/6 inhibitors is the standard first option in the management of advanced luminal breast cancer independently of disease extension. Classically, patients undergo multiple lines of ET ± targeted treatments until endocrine resistance occurs and palliative chemotherapy is proposed. Understanding endocrine resistance mechanisms and development of novel ET options is one of the main challenges in current clinical research. Another area of utmost interest is the improvement of post-endocrine therapeutic approaches. Among others, the development of antibody-drug conjugates (ADCs) is very promising, and some of these drugs will probably soon become a part of the therapeutic arsenal against this incurable disease. This review paper provides an overview of currently available treatment options in ER+/HER2- metastatic breast cancer and extensively discusses new approaches in late clinical development.

CDK inhibitors from past to present: A new wave of cancer therapy

Deregulation of the cell cycle machinery, which has been linked to dysregulation of cyclin-dependent kinases (CDKs), is a defining characteristic of cancer, eventually promoting abnormal proliferation that feeds tumorigenesis and disease development. In this regard, several CDK inhibitors (CDKIs) have been developed during the last few decades (1st, 2nd, and 3rd generation CDKIs) to inhibit cancer cell proliferation. 1st and 2nd generation CDKIs have not received much clinical attention for the treatment of cancer patients because of their limited specificity and high toxicity. However, the recent development of combination strategies allowed us to reduce the toxicity and side effects of these CDKIs, paving the way for their potential application in clinical settings. The 3rd generation CDKIs have yielded the most promising results at the preclinical and clinical levels, propelling them into the advanced stages of clinical trials against multiple malignancies, especially breast cancer, and revolutionizing traditional treatment strategies. In this review, we discuss the most-investigated candidates from the 1st, 2nd, and 3rd generations of CDKIs, their basic mechanisms of action, the reasons for their failure in the past, and their current clinical development for the treatment of different malignancies. Additionally, we briefly highlighted the most recent clinical trial results and advances in the development of 3rd generation FDA-approved selective CDK4/6 inhibitors that combat the most prevalent cancer. Overall, this review will provide a thorough knowledge of CDKIs from the past to the present, allowing researchers to rethink and develop innovative cancer therapeutic regimens.

CDK4/6 Inhibitors as Upfront Treatment in a Patient with Breast Cancer Presenting with a Clinical Critic Situation: A Case Report and Review of the Literature

CDK4/6 inhibitors have revolutionized the treatment algorithm of luminal metastatic breast cancer, becoming the recommended first-line therapy in association with endocrine therapy. However, due to its theoretically greater and more rapid tumor shrinkage, the upfront use of chemotherapy is considered in some clinical situations like visceral crisis. At the state of the art level, a paucity of data is available about the use of CDK4/6 inhibitors in patients presenting with visceral crisis or with life-threatening conditions since this population was historically excluded from clinical trials. In addition, data regarding direct comparison between combinations of chemotherapy and CDK4/6 inhibitors in terms of efficacy, rapidity of responses and long-term outcomes are lacking. We report the case of a 68-year-old woman with luminal metastatic breast cancer presenting at diagnosis with a critical and potentially life-threatening condition. The patient was treated with first-line Abemaciclib plus letrozole and achieved a rapid partial response with sudden clinical stabilization. Although the patient did not technically present with a visceral crisis, this case presentation also endorsed the upfront use of CDK4/6 inhibitor combinations in critical clinical situations in the absence of severe organ dysfunction and after multidisciplinary discussion.

Real world evidence study on treatment patterns and health resource utilization in patients with HR+/HER2- locally advanced or metastatic breast cancer in Korea

Objective

To understand current treatment patterns and health care resource utilization (HRU) of women with locally advanced or metastatic breast cancer (advanced breast cancer; ABC) in Korea overall and within patients who had progressed with prior endocrine therapy (as first-line treatment for metastatic disease) and patients with no prior systemic treatment (for advanced disease).

Methods

A chart review was conducted in 109 patients (women ≥ 18 years old with HR+/HER2- ABC diagnosed between 2015 and 2017) from 11 hospitals. Anonymized data on patient characteristics, treatment patterns and HRU was abstracted.

Results

Mean (range) age of all patients was 57.5 (40–81) years. Overall, the most common first-, second- and third-line systemic therapy after diagnosis of ABC were letrozole ± palbociclib (51%), endocrine therapy (ET)±everolimus (42%) or chemotherapy (ChT) (39%), and ChT (68%), respectively. In patients progressed with ET (n = 33) and those with no prior systemic treatment (n = 52), the most common first-line treatments were letrozole (82%) and letrozole + palbociclib (42%), respectively. The percentage of patients with at least one grade 3 or higher adverse event during first-line therapy was 93.1% vs 39.2% in patients on a ChT based regimen (N = 29) vs. ET (N = 74). Overall, oncologist visits, at an annual rate of 9.27 (95% CI: 8.87, 9.69) visits per month, and hospitalizations, with an annual rate of 0.44 (95% CI: 0.36, 0.54), and mean (SD) length of stay of 14.3 (10.32) days, were the key drivers of HRU.

Conclusions

These findings on real world HRU reflected clinical guidelines and severity of ABC. Results can inform future evaluations of new ABC treatments that estimate the health economic impact of their adoption in Korea.

Cost-effectiveness of ribociclib for premenopausal or perimenopausal women with HR+/HER2− advanced breast cancer: a Brazilian public health care system perspective

Introduction:

The MONALEESA-7 trial compared ribociclib plus endocrine therapy (ET) with placebo as first-line treatment of advanced luminal/HER2-negative breast cancer (ABC) in premenopausal and perimenopausal women (age <50 years) and showed significant benefits to progression-free survival and overall survival. This study aimed to compare the cost-effectiveness of ribociclib + ET versus ET alone in patients with ABC from the perspective of the Brazilian public national health system.

Methods:

We calculated the incremental cost-effectiveness ratio (ICER) using a Markov model with progression-free survival, post-progression survival, and death states. We expressed ICER as incremental costs per progression-free life-year (PFLY) and quality-adjusted life-year (QALY) gained in a 10-year time horizon. We used parametric survival distributions fit to MONALEESA-7 data to generate survival distributions for progression-free and post-progression survival. The largest British preference study in breast cancer served as the basis to estimate health-state utilities. We estimated direct costs (ABC treatment, follow-up, monitoring, and adverse events) using Brazilian-specific values from public sources. An expert consensus panel determined the resource patterns required. We applied annual discounts of 5% to costs and QALYs.

Results:

Ribociclib + ET resulted in an incremental gain of 1.03 PFLYs and 0.80 QALYs at a cost of $37,319.31. The ICER of ribociclib + ET versus ET was $36,379.41 per PFLY gained and $46,590.79 per QALY gained. In deterministic sensitivity analysis, results were primarily affected by the annual discount rate, followed by the cost of ribociclib. In probabilistic sensitivity analysis, simulations agreed with the base-case.

Conclusion:

Ribociclib increased PFLYs and QALYs in patients with HR+/HER2− ABC when added to ET. Because Brazil does not have a formally defined cost-effectiveness threshold, other domains need to be considered for incorporation decisions, such as disease burden and humanistic impact on this young, economically active population. These findings may be useful in discussions for incorporation of ribociclib into the Brazilian public health system.

Role of CDK4/6 inhibitors in patients with hormone receptor (HR)-positive, human epidermal receptor-2 negative (HER-2) metastatic breast cancer study protocol for a systematic review, network meta-analysis and cost-effectiveness analysis

INTRODUCTION

It is currently unclear which cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, combined with endocrine therapy, is the preferred treatment approach in patients with hormone receptor (HR)-positive, human epidermal receptor-2 (HER2) negative metastatic breast cancer. The aim of this study was to evaluate the existing evidence for the comparative efficacy, safety and cost-effectiveness of different CDK4/6 inhibitors for metastatic breast cancer in first-line and second-line settings.

METHODS AND ANALYSIS

We will systematically conduct a literature search in Embase, PubMed and the Cochrane Library and additional searches by handsearching citations of previous systematic reviews. We will also screen major conference proceedings (American Society of Clinical Oncology, European Society of Medical Oncology and San Antonio Breast Cancer Symposium). Preliminary scoping searches were conducted in July 2021, but the search will be updated when new trials are available. The primary outcome was progression-free survival. The secondary outcomes were overall survival, objective response rates, grade 3-4 haematological and non-haematological toxicities, quality-adjusted life years and incremental cost-effectiveness ratios. The risk of bias will be assessed by Cochrane risk of bias tools, and the quality of evidence will be assessed by the Grading of Recommendations Assessment, Development and Evaluation. Subgroup analyses and sensitivity analyses will be performed to further confirm our findings. In addition, one-way sensitivity analysis and probabilistic sensitivity analyses will be conducted to determine uncertainty.

ETHICS AND DISSEMINATION

This study does not require ethics approval as only secondary data will be collected. The results of our study will provide an overview of the current level of CDK4/6 inhibitors for patients with HR-positive, HER2-negative metastatic breast cancer, and undertake subgroup analyses to explore variables that might affect these effects. The results of this study will be presented at an international clinical conference and published in a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42021266597.

The chemistry and biology of natural ribomimetics and related compounds

Natural ribomimetics represent an important group of specialized metabolites with significant biological activities. Many of the activities, e.g., inhibition of seryl-tRNA synthetases, glycosidases, or ribosomes, are manifestations of their structural resemblance to ribose or related sugars, which play roles in the structural, physiological, and/or reproductive functions of living organisms. Recent studies on the biosynthesis and biological activities of some natural ribomimetics have expanded our understanding on how they are made in nature and why they have great potential as pharmaceutically relevant products. This review article highlights the discovery, biological activities, biosynthesis, and development of this intriguing class of natural products.

NCCN Guidelines Updates: Management of Patients With HER2-Negative Breast Cancer

Treatment for metastatic HER2-negative breast cancer is becoming increasingly individualized as more of the tumor landscape is described and drugs are developed to target its pathways. Survival can be prolonged by CDK4/6 inhibitors in patients with hormone receptor–positive tumors and by immunotherapy in those with triple-negative disease. In patients with BRCA1/2 mutations, PARP inhibitors delay disease progression. Antibody–drug conjugates are expected to become critical components of the treatment landscape, and targeted drugs are proving to benefit small subsets of patients.

How to Treat HR+/HER2- Metastatic Breast Cancer Patients after CDK4/6 Inhibitors: An Unfinished Story

CDK4/6 inhibitors in association with endocrine therapy represent the best therapeutic choice for either endocrine-sensitive or resistant hormone-receptor-positive advanced breast cancer patients. On the contrary, the optimal therapeutic strategy after the failure of CDK4/6 inhibitors-based treatment still remains an open question worldwide. In this review, we analyze the most studied mechanisms of resistance to CDK4/6 inhibitors treatment, as well as the most significant results of retrospective and prospective trials in the setting of progression after CDK4/6 inhibitors, to provide the reader a comprehensive overview from both a preclinical and especially a clinical perspective. In our opinion, an approach based on a deeper knowledge of resistance mechanisms to CDK4/6 inhibitors, but also on a careful analysis of what is done in clinical practice, can lead to a better definition of prospective randomized trials, to implement a personalized sequence approach, based on molecular analyses.

Mechanisms of Resistance to CDK4/6 Blockade in Advanced Hormone Receptor-positive, HER2-negative Breast Cancer and Emerging Therapeutic Opportunities

The cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have become the standard of care, in combination with antiestrogen therapy, for patients with hormone receptor-positive (HR⁺)/HER2^- advanced breast cancer. Various preclinical and translational research efforts have begun to shed light on the genomic and molecular landscape of resistance to these agents. Drivers of resistance to CDK4/6i therapy can be broadly subdivided into alterations impacting cell-cycle mediators and activation of oncogenic signal transduction pathways. The resistance drivers with the best translational evidence supporting their putative role have been identified via next-generation sequencing of resistant tumor biopsies in the clinic and validated in laboratory models of HR⁺ breast cancer. Despite the diverse landscape of resistance, several common, therapeutically actionable resistance nodes have been identified, including the mitotic spindle regulator Aurora Kinase A, as well as the AKT and MAPK signaling pathways. Based upon these insights, precision-guided therapeutic strategies are under active clinical development. This review will highlight the emerging evidence, in the clinic and in the laboratory, implicating this diverse spectrum of molecular resistance drivers.

Which Clinicopathologic Parameters Suggest Primary Resistance to Palbociclib in Combination With Letrozole as the First-Line Treatment for Hormone Receptor-Positive, HER2-Negative Advanced Breast Cancer?

In this study, we evaluated clinical parameters to predict the primary resistance of palbociclib in combination with endocrine therapy as the first-line treatment in patients with hormone receptor (HR)+, human epidermal growth factor receptor 2 (HER2)- metastatic breast cancer (MBC). We performed a data analysis of patients diagnosed with HR+, HER2-MBC who received palbociclib plus letrozole as the first-line treatment in the metastatic setting from the clinical data warehouse in Samsung Medical Center. In this study, 305 patients were included in the final data analysis. The median follow-up duration was 31 months, and we observed 123 cases of disease progression. The median progression-free survival (PFS) was 28.7 months, and 38 patients (12.5%) had less than a 6-month PFS. The multivariate analysis suggested that primary resistance to adjuvant endocrine therapy (ET) (hazard ratio: 1.91), presence of liver metastasis (hazard ratio: 2.17), initial elevation of serum CA-15-3 (hazard ratio: 1.99), weak positivity of estrogen receptor (ER) (hazard ratio: 2.28), Ki-67 3+ or 4+ (hazard ratios: 2.58 and 10.28), and presence of mutation (hazard ratio: 9.59) were associated with a short PFS duration. A further prediction model was developed with data from 256 patients and 33 cases of disease progression in 6 months. This model included five factors-primary resistance to adjuvant ET (odds ratio, OR: 1.14), liver metastasis (OR: 1.56), initial CA-15-3 elevation (OR: 1.51), weak ER expression (OR: 2.22), and BRCA2 mutation (OR: 2.85)-and the area under the receiver operating characteristic curve was 0.842 (95% CI: 0.775, 0.909; p < 0.001). Finally, we divided them into four risk groups according to the prediction model with the five risk factors. These four groups had different PFS (p < 0.001) and primary resistance of palbociclib with letrozole [OR of group 2 vs. group 1 (ref): 2.18 (p = 0.002), OR of group 3: 3.91 (p < 0.001), and OR of group 4: 4.25 (p < 0.001)]. We developed a prediction model of primary resistance to palbociclib with letrozole as the first-line treatment for HR+, HER2-MBC. Our prediction model might be helpful for considering the first-line treatment strategies. Further well-designed clinical trials would be warranted to validate our prediction model.

Overall survival in patients with hormone receptor-positive, HER2-negative, advanced or metastatic breast cancer treated with a cyclin-dependent kinase 4/6 inhibitor plus fulvestrant: a US Food and Drug Administration pooled analysis

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDKIs) are oral targeted agents approved for use in combination with endocrine therapy as first-line or second-line treatment of patients with hormone receptor-positive, HER2-negative, advanced or metastatic breast cancer. We previously reported the pooled analyses of progression-free survival in patients in specific clinicopathological subgroups, all of whom received consistent benefit from the addition of a CDKI to hormonal therapy. Here, we report the pooled overall survival results in patients treated with a CDKI and fulvestrant.

METHODS

In this exploratory analysis, we pooled individual patient data from three phase 3 randomised trials of CDKI or placebo in combination with fulvestrant in patients with breast cancer submitted to the US Food and Drug Administration and approved before Aug 1, 2020, in support of marketing applications. All analysed patients were aged at least 18 years, had an Eastern Cooperative Oncology Group performance status of 0-1, had hormone receptor-positive, HER2-negative advanced or metastatic breast cancer, and received at least one dose of CDKI or placebo in combination with fulvestrant. The median overall survival was estimated using Kaplan-Meier methods, and hazard ratios (HRs) with corresponding 95% CIs were estimated using Cox regression models. Patients were analysed collectively, by number of previous lines of systemic endocrine therapy in any disease setting (first-line or endocrine naive vs second-line and later), and in various clinicopathological subgroups of interest. The estimated median overall survival was not reported by group when the pooled population included patients treated across lines of therapy because of potential patient heterogeneity. All results presented are considered exploratory and hypothesis generating.

FINDINGS

Across the three pooled trials, 1960 patients were randomly assigned between Oct 7, 2013, and June 10, 2016 (12 patients were not treated and 1296 [66%] patients were randomly assigned to CDKI and 652 [33%] to placebo). In all treated patients (n=1948), the estimated HR for overall survival was 0·77 (95% CI 0·68-0·88), with a median follow-up of 43·7 months (IQR 37·8-47·7) and deaths in 935 (48%) of the 1948 patients. The difference in estimated median overall survival was 7·1 months, favouring CDKIs. In patients who received CDKIs or placebo in combination with fulvestrant as first-line systemic endocrine therapy (two trials; n=396), the estimated HR for overall survival was 0·74 (95% CI 0·52-1·07), with a median follow-up of 39·4 months (IQR 37·0-42·2). 123 (31%) of these patients died. The difference in estimated median overall survival could not be calculated because median overall survival was not estimable (95% CI 50·9-not estimable) in the CDKI group and was 45·7 months (95% CI 41·7-not estimable) in the placebo group. In patients who received CDKIs or placebo in combination with fulvestrant as second-line or later systemic endocrine therapy (three trials; n=1552), the estimated HR for overall survival was 0·77 (95% CI 0·67-0·89), with a median follow-up of 45·1 months (95% CI 39·2-48·5). 812 (52%) of these patients died. The difference in estimated median overall survival was 7·0 months, favouring CDKIs.

INTERPRETATION

The addition of CDKIs to fulvestrant resulted in a consistent overall survival benefit in all pooled patients and within most clinicopathological subgroups of interest. These findings support the existing standard of care of CDKIs plus fulvestrant for the treatment of patients with hormone receptor-positive, HER2-negative, advanced breast cancer.

FUNDING

None.