A genome-wide CRISPR/Cas9 knockout screen identifies SEMA3F gene for resistance to cyclin-dependent kinase 4 and 6 inhibitors in breast cancer.

BACKGROUND: Palbociclib is a cell-cycle targeted small molecule agent used as one of the standards of care in combination with endocrine therapy for patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. Although several gene alterations such as loss of Rb gene and amplification of p16 gene are known to be conventional resistance mechanisms to cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, the comprehensive landscape of resistance is not yet fully elucidated. The purpose of this study is to identify the novel resistant genes to the CDK4/6 inhibitors in HR-positive HER2-negative breast cancer. METHODS: The whole genome knockout screen using CRISPR/Cas9 genome editing was conducted in MCF7 to identify resistant genes to palbociclib. The candidate genes for resistance were selected by NGS analysis and GSEA analysis and validated by cell viability assay and mouse xenograft models. RESULTS: We identified eight genes including RET, TIRAP, GNRH1, SEMA3F, SEMA5A, GATA4, NOD1, SSTR1 as candidate genes from the whole genome knockout screen. Among those, knockdown of SEMA3F by siRNA significantly and consistently increased the cell viability in the presence of CDK4/6 inhibitors in vitro and in vivo. Furthermore, the level of p-Rb was maintained in the palbociclib treated SEMA3F-downregulated cells, indicating that the resistance is driven by increased activity of cyclin kinases. CONCLUSION: Our observation provided the first evidence of SEMA3F as a regulator of sensitivity to CDK4/6 inhibitors in breast cancer. The detailed mechanisms of resistance deserve further functional studies to develop the better strategy to overcome resistance in CDK4/6 inhibitors.

Updates in Systemic Treatment of Hormone Receptor-Positive Early-Stage Breast Cancer.

OPINION STATEMENT: Hormone-receptor positive (HR +) and human epidermal growth factor receptor 2 (HER2) negative early breast cancer (eBC) is a heterogeneous disease with several contributing factors for increased risk of recurrence, including tumor features, individual biomarkers, and genomic risk. The current standard approach in the management of HR + /HER2neg eBC includes chemotherapy and endocrine therapy (ET), and additional therapies based on risk profile, menopausal status, and genetics are sometimes appropriate. The risk of recurrence is more pronounced in patients with high-risk eBC including large tumor size, nodal involvement, high proliferative index, and genetic predisposition. In premenopausal patients with high-risk eBC, ovarian function suppression in combination with adjuvant ET improves survival. In postmenopausal patients, extended aromatase inhibitor (AI) therapy can be considered. Recent trials have identified novel treatment approaches to reduce the risk of recurrence in high-risk HR + /HER2neg eBC including the addition of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors to adjuvant ET. For patients with germline BRCA1/BRCA2 mutations, adjuvant poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitors have been shown to improve overall survival (OS). However, despite these recent advances, the risk of recurrence remains substantial, highlighting an area of unmet need. There are several ongoing clinical trials further investigating the role of CDK 4/6 inhibitors and immunotherapy in high-risk HR + /HER2neg eBC.

Synergistic effect of bazedoxifene and abemaciclib co­treatment in triple­negative breast cancer cells in vitro.

Triple-negative breast cancer (TNBC) is an aggressive disease with the capability of metastasizing quickly. However, treatment options for patients with TNBC still remain limited. CDK4/6 inhibitors have been approved by the U.S. Food and Drug Administration and are administered for the treatment of hormone receptor-positive breast cancer subtypes, but not yet for TNBC. Although pre-clinical research is being conducted on their efficacy in treating TNBC, acquired resistance to CDK4/6 inhibitors is now a growing clinical problem. One of the identified resistance mechanisms is through the IL-6/STAT3 signaling pathway. In the present study, the CDK4/6 inhibitor, abemaciclib, was tested in combination with the IL-6 inhibitor, bazedoxifene, on human (SUM159 and MDA-MB-231) and murine (4T1) TNBC cell lines. Both abemaciclib and bazedoxifene monotherapies inhibited cell cycle progression and cell viability, migration and invasion, and induced apoptosis; however, the combination treatment exerted a greater effect than either monotherapy. These findings support the concept of CDK4/6 and IL-6 dual inhibition as a novel targeted therapy against TNBC.

Advances in the mechanism of CDK4/6 inhibitor resistance in HR+/HER2- breast cancer.

Among women, breast cancer is the most prevalent form of a malignant tumour. Among the subtypes of breast cancer, hormone receptor (HR) positive and human epidermal growth factor receptor (HER2) negative kinds make up the biggest proportion. The advent of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, which are dependent on cell cycle proteins, has greatly enhanced the prognosis of patients with advanced HR+/HER2- breast cancer. This is a specific treatment that stops the growth of cancer cells by preventing them from dividing. Nevertheless, the drug resistance of the disease unavoidably impacts the effectiveness of treatment and the prognosis of patients. This report provides a thorough analysis of the current research advancements about the resistance mechanism of CDK4/6 inhibitors in HR+/HER2- breast cancer. It presents an in-depth discussion from numerous viewpoints, such as aberrant cell cycle regulation and changes in signalling pathways. In response to the drug resistance problem, subsequent treatment strategies are also being explored, including switching to other CDK4/6 inhibitor drugs, a combination of novel endocrine therapeutic agents, an optimal combination of targeted therapies and switching to chemotherapy. An in-depth study of the resistance mechanism can assist in identifying creative tactics that can overcome or postpone drug resistance, alleviate the problem of restricted treatment strategies following drug resistance and enhance the prognosis of patients.

Capivasertib and fulvestrant for patients with HR-positive/HER2-negative advanced breast cancer: analysis of the subgroup of patients from Japan in the phase 3 CAPItello-291 trial.

BACKGROUND: In CAPItello-291, capivasertib-fulvestrant significantly improved progression-free survival (PFS) versus placebo-fulvestrant in the overall and PIK3CA/AKT1/PTEN-altered population with hormone receptor-positive (HR-positive)/human epidermal growth factor receptor 2-negative (HER2-negative) advanced breast cancer. Capivasertib-fulvestrant is approved in Japan for the treatment of patients with one or more tumor biomarker alterations (PIK3CA, AKT1 or PTEN). Here, we report outcomes in the CAPItello-291 subgroup of patients from Japan. METHODS: Adults with HR-positive/HER2-negative advanced breast cancer whose disease had relapsed or progressed during or after treatment with an aromatase inhibitor, with or without previous cyclin-dependent kinase 4/6 (CDK4/6) inhibitor therapy, were randomly assigned (1:1 ratio) to receive capivasertib or placebo, plus fulvestrant. The dual primary endpoint was investigator-assessed PFS in the overall and PIK3CA/AKT1/PTEN-altered population. Safety was a secondary endpoint. RESULTS: Of 708 patients randomized in CAPItello-291, 78 were from Japan (37 randomized to capivasertib-fulvestrant and 41 to placebo-fulvestrant). In the Japan subgroup, PFS numerically favored the capivasertib-fulvestrant arm (hazard ratio 0.73; 95% CI 0.40-1.28), consistent with the analysis of PFS in the global population. Similarly, in the Japan subgroup of patients with PIK3CA/AKT1/PTEN-altered tumors, PFS favored the capivasertib-fulvestrant arm (hazard ratio 0.65; 95% CI 0.29-1.39), consistent with the global population. The adverse event profile of capivasertib-fulvestrant in the Japan subgroup was broadly similar to that in the global population; no new safety concerns were identified. CONCLUSION: Outcomes in the Japan subgroup were broadly similar to those of the global population, supporting the clinical benefit of capivasertib-fulvestrant in treating HR-positive/HER2-negative advanced breast cancer that has progressed on, or after, an endocrine-based regimen.

Clinical Outcomes of Patients Treated with Ribociclib in Combination with Aromatase Inhibitors or Fulvestrant for HR-Positive, HER2-Negative Metastatic Breast Cancer, Real-World Data from a Low-Resourced Country.

Background: Cyclin-dependent kinase (CDK) 4/6 inhibitors have revolutionized the treatment landscape of hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2 -) metastatic breast cancer (MBC). Here, we present the real-world clinical outcomes and toxicity data of patients treated at a single cancer center. Methods: A retrospective analysis was conducted on patients with HR+/HER2- MBC treated with ribociclib plus endocrine therapy (ET). Outcomes measured included progression-free survival (PFS), overall survival (OS), and adverse events. Results: A total of 356 patients (median age 52, range 27-91 years) were enrolled, all with metastatic disease; 204 (57.5%) had de novo metastasis, and 183 (51.4%) had visceral metastasis. Ribociclib was combined with aromatase inhibitors in 321 patients (90.2%) and with fulvestrant in 35 patients (9.8%). Dose reduction was needed in 101 patients (28.4%), primarily due to neutropenia (21.3%) and abnormal liver enzymes (5.9%). After a median follow-up of 36.3 months, median PFS was 27.3 months (95% CI: 21.3-31.7). PFS was significantly better in patients receiving ribociclib as first-line therapy (32.1 months, 95% CI: 27.7-42.1, p < 0.0001) and those with non-visceral metastasis (38.6 months, 95% CI: 29.8-NR, p < 0.0001). Similarly, OS was significantly better in first-line treatment (48.6 months, 95% CI: 39.1-NR) and non-visceral metastasis cases (NR, 95% CI: 40.6-NR, p < 0.0001). No significant differences in 3-year PFS and OS were found between patients with and without dose reductions. Conclusion: In real-world settings, and away from the stringency of controlled clinical trials, endocrine therapy in combination with ribociclib in patients with HR-positive/HER2-negative MBC is an effective and well-tolerated therapy with a manageable toxicity profile and a low drug discontinuation rate. Dose reduction due to toxicity did not worsen the outcome.

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.

The different sequences of CDK4/6 inhibitor and mTOR inhibitor in HR+/HER2-advanced breast cancer: A multicenter real-world study.

Background: Cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) and everolimus (EVE) are effective for patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). However, the efficacy of different sequences of CDK4/6i and EVE are largely unknown. The study aimed to explore the efficacy of different sequences in China. Methods: 146 patients with HR+/HER2- MBC who received both CDK4/6i and EVE in salvage setting were collected. Objective response rate (ORR), clinical benefit rate (CBR), progression-free survival (PFS), and overall survival (OS) were investigated. Results: 56 patients received CDK4/6i prior to EVE (Group A), 90 patients received CDK4/6i subsequent to EVE (Group B). The median PFS of CDK4/6i and EVE in Group A vs Group B were 8.4m and 2.5m vs 4.6m and 6.1m respectively. The total PFS of first-line and second-line endocrine therapy were not different between Group A and Group B [13.1m vs 17.7m (P = 0.330, HR = 0.738, 95%CI: 0.399-1.365)]. The 5y OS of patients in Group A or Group B were 62.0 % vs 57.4 %, P = 0.569. Conclusions: We found that no matter CDK4/6i or EVE was used first, the survival were not significantly different between Group A and Group B. Both can be clinical options.

Adverse event profiles of CDK4/6 inhibitors: data mining and disproportionality analysis of the FDA adverse event reporting system.

Background: Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are targeted therapies designed to selectively block CDK4/6, crucial regulators of the cell cycle. These inhibitors play a pivotal role in restoring cell cycle control, particularly in breast cancer cases marked by abnormal CDK regulation, ultimately inhibiting uncontrolled cell division and tumor growth. Objectives: This analysis aimed to comprehensively examine adverse effects in CDK4/6 inhibitors using the United States Food and Drug Administration (FDA) Adverse Event Reporting System (FAERS) database. Design: Disproportionality analysis was conducted to analyze the adverse event (AE) reports related to CDK4/6 inhibitor submitted to the FAERS database. Methods: We collected AE reports regarding palbociclib, ribociclib, abemaciclib, trilaciclib, and dalpiciclib submitted to the FAERS from 2015Q1 to 2023Q1. We used the system organ class and the Standardized MedDRA Query to perform a comprehensive search for AEs at the preferred term (PT) level, using case reports as our data source. After removing duplicate reports, we performed disproportionality analysis and sensitivity analysis to identify safety signals. Results: A total of 85,635 reports encompassing 280,211 AEs were extracted for analysis. Among 3681 scrutinized PTs, approximately 484 were detected as statistically significant signals associated with CDK4/6 inhibitors. It was noteworthy that palbociclib and ribociclib had comparable safety profiles, whereas abemaciclib exhibited distinctive safety patterns. Notably, our analysis found novel safety signals linked to CDK4/6 inhibitors, including nail-related disorders such as onychoclasis, nail disorder, and nail discoloration, and psychiatric concerns, including eating disorders and emotional disorder. Conclusion: Overall, the present study identified several new safety signals of CDK4/6 inhibitors, as well as differences among various drugs within the CDK4/6 category, through the use of the FDA FAERS, which deserve more careful monitoring in the clinic.

Introduction: An adverse event (AE) refers to any undesirable or harmful occurrence that happens to an individual during or after the use of a medical product or intervention. These events are typically reported to regulatory authorities, such as the Food and Drug Administration (FDA), to ensure the safety and effectiveness of medical products. The United States Food and Drug Administration Adverse Event Reporting System (FAERS) database plays a pivotal role in identifying these adverse events. Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are a class of drugs used to treat certain types of cancer by inhibiting the growth and division of cancer cells. This study investigated the safety signals related to CDK4/6 inhibitors, including palbociclib, ribociclib, abemaciclib, and trilaciclib, by using the FAERS database. Methods: We collected AE reports associated with CDK4/6 inhibitors that were submitted to the FAERS database between the first quarter of 2015 and the first quarter of 2023. Reporting odds ratio (ROR) method was used identify signals of AEs. Results: 85,635 AE reports were identified, approximately 484 AE terms were identified as positive signals. Palbociclib and ribociclib had similar safety profiles, while abemaciclib showed a unique pattern. Our analysis also revealed previously unreported AEs, including nail-related disorders such as onychoclasis, nail disorder and nail discolouration. Psychiatric concerns such as eating disorders and emotional disorder were also identified. Conclusion: We discovered important safety concerns related to CDK4/6 inhibitors. Some of these concerns were consistent with previous studies, while nail-related disorders, eating disorder and emotional disorder were new and not mentioned in the drug labels or existing literature. Our findings may help physicians and pharmacists to weigh the risks and benefits of using CDK4/6 inhibitors in clinical practice.

A study on the adverse effects of CDK4/6 inhibitors.

Adjuvant and neoadjuvant therapy with or without CDK4/6 inhibitors in HR+/HER2- early breast cancer: a systematic review and meta-analysis.

Background: The combination of cyclin-dependent kinases 4/6 (CDK4/6) inhibitors and endocrine therapy is the standard treatment for patients with hormone receptor-positive (HR+)/HER2-negative (HER2-) advanced breast cancer. However, the role of CDK4/6 inhibitors in early breast cancer remains controversial. Methods: This study aimed to evaluate the efficacy and safety of CDK4/6 inhibitors combined with endocrine therapy versus endocrine therapy alone in patients with HR+, HER2- early breast cancer. A systematic review of Cochrane, PubMed and EMBASE databases was conducted. The efficacy endpoints of adjuvant therapy were invasive disease-free survival (IDFS), overall survival (OS) and distant relapse-free survival (DRFS). The efficacy endpoint included complete cell cycle arrest (CCCA) and complete pathologic response (PCR) with neoadjuvant therapy. Grade 3/4 adverse events (AEs) were assessed as safety outcomes. Results: Eight randomized controlled trials (RCTs) were included in the study. CDK4/6 inhibitors combined with endocrine therapy showed a significant improvement in IDFS (hazard ratio (HR) = 0.81, 95% confidence interval (CI) = 0.68-0.97, P = 0.024), but not DRFS (HR = 0.84, 95% CI = 0.56-1.29, P = 0.106) or OS (HR = 0.96, 95% CI = 0.77-1.19, P = 0.692) in adjuvant therapy. In the neoadjuvant therapy setting, CDK4/6 inhibitors improved CCCA compared with the control group (RR = 2.08, 95% CI = 1.33-3.26, P = 0.001). The risk of 3/4 grade AEs increased significantly with the addition of CDK4/6 inhibitors to endocrine therapy. Conclusion: The addition of CDK4/6 inhibitors in HR+/HER2- early breast cancer patients significantly improved IDFS in adjuvant therapy and CCCA in neoadjuvant. However, CDK4/6 inhibitors also showed significant toxicities during therapy. Systematic Review Registration: Identifier CRD42024530704.

The impact of body mass index on the progression-free survival of CDK 4/6 inhibitors in metastatic breast cancer patients.

Aim: Endocrine therapy (ET) plus cyclin-dependent kinase (CDK) 4/6 inhibitors is a standard treatment for hormone receptor (HR) positive HER-2-negative metastatic breast cancer patients. In this study, we aimed to investigate the effect of body mass index (BMI) on progression-free survival (PFS) in patients receiving ET plus CDK 4/6 inhibitors.Materials & methods: Patients with metastatic HR-positive breast cancer receiving CDK 4/6 inhibitors were included in the study. A total of 116 patients were retrospectively evaluated. Patients were divided into three groups according to BMI level: normal weight (group 1) 18.5-24.9 kg/m2, overweight (group 2) 25-29.9 kg/m2 and obese (group 3): ≥30 kg/m2. Median follow-up was 10.83 months. Comparisons of PFS and BMI categories were performed by Kaplan-Meier curve and log-rank test.Results: PFS was 9.3 (5.3-13.4) months in normal weight patients and 11.1 (9.7-12.56) months in obese patients and was not reached in overweight patients. This difference was statistically significant (p = 0.02).Conclusion: Low BMI has been shown to have a negative prognostic effect on survival in patients with metastatic breast cancer and overweight patients had a longer PFS.

[Box: see text].

Prognosis in HR-positive metastatic breast cancer with HER2-low versus HER2-zero treated with CDK4/6 inhibitor and endocrine therapy: a meta-analysis.

Background: The combination of CDK4/6 inhibitors (CDK4/6i) and endocrine therapy (ET) is currently the standard first-line treatment for patients with metastatic hormone receptor positive (HR+), and HER2-negative (HER2-) breast cancer. However, the impact of HER2 status on the prognosis of patients receiving CDK4/6i and ET remains unclear. The meta-analysis was conducted to evaluate different outcomes between HER2-low and HER2-zero patients in advanced HR+ breast cancer receiving CDK4/6i and ET. Methods: A systematic search was performed in PubMed and EMBASE databases for relevant published literature. Objective response rate (ORR), overall survival (OS), and progression-free survival (PFS) were pooled by fixed or random effects models. Results: Overall, 12 studies with 3567 patients were eligible for analysis. The pooled analysis suggested that no significant differences were observed in terms of ORR and OS between HER2-low and HER2-zero patients who underwent CDK4/6i and ET. Similarly, no significant difference in PFS was found between HER2-low and HER2-zero patients who underwent post-line CDK4/6i and ET or first-line Palbociclib and ET. However, in patients who received mixed-line (not a single treatment line) or first-line CDK4/6i and ET, the PFS was significantly shorter in the HER2-low subgroup than in the HER2-zero subgroup (mixed-line: HR = 1.36; 95% CI = 1.11-1.65; P = 0.002; first-line: HR = 1.14; 95% CI = 1.01-1.28; P = 0.04). A similar phenomenon was observed in patients who received mixed-line or post-line Palbociclib and ET (mixed-line: HR = 1.60; 95% CI = 1.09-2.34; P = 0.02; post-line: HR = 1.43; 95% CI = 1.03-2.00; P = 0.03). Conclusion: These results indicated that HER2-low status did not have a significant association with ORR and OS, but it may have a worse impact on PFS in patients who received mixed-line or first-line CDK4/6i and ET, as well as mixed-line or post-line palbociclib plus ET.

Real-World Analysis of Breast Cancer Patients Qualifying for Adjuvant CDK4/6 Inhibitors.

BACKGROUND: Adjuvant CDK4/6 inhibitors abemaciclib and ribociclib improved disease-free survival (DFS) added to endocrine therapy in hormone receptor (HR)-positive HER2-negative early breast cancer (EBC), in monarchE (NCT03155997) and NATALEE (NCT03701334) trials respectively. We assessed the proportion and outcome of EBC patients qualifying for adjuvant CDK4/6 inhibitors in the real-world. METHODS: Consecutive female patients with HR-positive HER2-negative EBC between 1997 and 2017 from the Australian Capital Territory and South-East New South Wales Breast Cancer Treatment Group registry were analyzed. Patients eligible for abemaciclib had ≥4 axillary nodes involved or 1-3 nodes plus primary >5 cm or grade 3. Ribociclib eligibility was defined as node-positive and node-negative with primary >5 cm or >2 cm grade 3. RESULTS: Of 3840 patients, 671 (17.5%) were abemaciclib-eligible and 1587 (41.3%) ribociclib-eligible . The 5-year DFS was 77% and 94% in abemaciclib-eligible and noneligible registry patients respectively (HR 2.6, 95% CI 2.26-3.05, P < .001). The 5-year DFS was 86% and 97% in ribociclib-eligible and noneligible registry patients respectively (HR 1.92, 95% CI 1.67-2.19, P < .001). Compared with monarchE trial patients, abemaciclib-eligible registry patients were older (median 55 years in registry vs. 51 years in trial), with lower nodal burden (≥4 nodes in 44% in registry vs. 60% in trial). There were more stage III cancers in NATALEE trial patients (60%) than ribociclib-eligible registry patients (24%). CONCLUSIONS: Many women with EBC will qualify for adjuvant CDK4/6 inhibitors (17.5% abemaciclib, 41.3% ribociclib) with resource and workforce implications. In the real-world setting, a greater proportion of adjuvant CDK4/6-eligible patients have lower stage disease, therefore the absolute benefit from treatment may be smaller than estimated by the trials.

Combined inhibition of CDK4/6 and AKT is highly effective against the luminal androgen receptor (LAR) subtype of triple negative breast cancer.

Luminal Androgen Receptor (LAR) triple-negative breast cancers (TNBC) express androgen receptors (AR), exhibit high frequency of PIK3CA mutations and intact RB. Herein, we investigated combined blockade of the CDK4/6 and PI3K signaling with palbociclib, alpelisib, and capivasertib, which inhibit CDK4/6, PI3Kα, and AKT1-3, respectively. The combination of palbociclib/capivasertib, but not palbociclib/alpelisib, synergistically inhibited proliferation of MDA-MB-453 and MFM-223 LAR cells [synergy score 7.34 (p = 5.81x10-11) and 4.78 (p = 0.012), respectively]. The AR antagonist enzalutamide was inactive against MDA-MB-453, MFM-223, and CAL148 cells and did not enhance the efficacy of either combination. Palbociclib/capivasertib inhibited growth of LAR patient-derived xenografts more potently than palbociclib/alpelisib. Treatment of LAR cells with palbociclib suppressed phosphorylated-RB and resulted in adaptive phosphorylation/activation of S473 pAKT and AKT substrates GSK3ß, PRAS40, and FoxO3a. Capivasertib blocked palbociclib-induced phosphorylation of AKT substrates more potently than alpelisib. Treatment with PI3Kß inhibitors did not block phosphorylation of AKT substrates, suggesting that PI3Kß did not mediate the adaptive response to CDK4/6 inhibition. Phosphokinase arrays of MDA-MB-453 cells treated with palbociclib showed time-dependent upregulation of PDGFRß, GSK3ß, STAT3, and STAT6. RNA silencing of PDGFRß in palbociclib-treated MDA-MB-453 and MFM-223 cells blocked the upregulation of S473 pAKT, suggesting that the adaptive response to CDK4/6 blockade involves PDGFRß signaling. Finally, treatment with palbociclib and the PDGFR inhibitor CP637451 arrested growth of MDA-MB-453 and MFM-223 cells to the same degree as palbociclib/capivasertib. These findings support testing the combination of CDK4/6 and AKT inhibitors in patients with LAR TNBC, and further investigation of PDGFR antagonists in this breast cancer subtype.

Abemaciclib increases the risk of venous thromboembolism in breast cancer: Integrate meta-analysis, pharmacovigilance database analysis, and in vitro validation.

BACKGROUND: Recently, cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have emerged as a novel treatment strategy for breast cancer. However, increasing reports of CDK4/6i-associated venous thromboembolism (VTE) have garnered attention. This study assessed CDK4/6i-associated VTE in breast cancer, and examined the effect of CDK4/6i on platelet/coagulation function for the first time in vitro. METHODS: PubMed and Embase databases were searched for studies published from the establishment of the database to December 31, 2022 for randomized controlled trials (RCTs) and real-world studies of CDK4/6i in patients with breast cancer, and the data obtained from the included studies were used for meta-analysis. A disproportionality analysis by extracting adverse drug reaction signals of CDK4/6i-associated VTE from the FDA Adverse Event Reporting System (FAERS) database was also conducted. Additionally, the in vitro effect of CDK4/6i on platelet function was assessed based on platelet aggregation tests and flow cytometry, and coagulation function was assessed based on the blood clotting function test. FINDINGS: A total of 16,903 patients in 13 RCTs and 6,490 patients in 9 real-world studies were included in the meta-analysis. In RCTs, VTE occurred in 193 (2.1 %) and 55 (0.7 %) patients in the CDK4/6i and control groups, respectively. In real-world studies, the aggregate incidence rate of VTE was 4.2 % (95 % CI: 2.1, 6.3). The meta-analysis of RCTs revealed that abemaciclib (Odds ratio [OR]: 4.40 [95 % CI: 2.74,7.05], p < 0.001) and palbociclib (OR: 2.35 [95 % CI: 1.34, 4.12], p < 0.01) significantly increased the risk of VTE in patients with breast cancer compared to placebo. FAERS database analysis revealed that abemaciclib (reporting odds ratio [ROR]: 1.63 [95 % CI: 1.36, 1.97]; IC025: 0.67) and ribociclib (ROR: 1.17 [95 % CI: 1.0, 1.39]; IC025: 0.18) demonstrated a significantly increased signal of VTE. Similarly, findings from in vitro experiments demonstrated that abemaciclib enhanced agonist-induced platelet activation, especially when collagen was used as the inducer, and this effect became more prominent with increasing its concentration. INTERPRETATION: Use of abemaciclib may increase the risk of VTE in patients with breast cancer, which may be partially attributed to the effect of abemaciclib on platelet function. Close monitoring of VTE occurrence is highly recommended while using abemaciclib, especially in patients at a high risk of VTE.

Neutrophil-to-lymphocyte ratio at the end of treatment with CDK4/6 inhibitors is an independent prognostic factor for ER-positive HER2-negative advanced breast cancer.

PURPOSE: The aim of this study was to elucidate the clinical significance of peripheral blood biomarkers, including absolute lymphocyte count (ALC) and neutrophil-to-lymphocyte ratio (NLR), at the end of treatment (EOT) with CDK4/6 inhibitors abemaciclib and palbociclib in patients with estrogen receptor-positive human epidermal growth factor receptor 2-negative advanced breast cancer. METHODS: We included 67 patients treated with fulvestrant plus abemaciclib or palbociclib. Overall survival (OS) since the EOT with CDK/4/6 inhibitors was compared in relation to the levels of ALC and NLR. The cut-off values of ALC and NLR were set at 1000/µL and 3, respectively. RESULTS: Patients with a high ALC at EOT showed significantly longer OS than those with a low ALC (p = 0.0358). Moreover, patients with a low NLR at EOT showed significantly longer OS than those with a high NLR at EOT (p = 0.0044). Looking at the changes of ALC and NLR between baseline and the EOT, patients with a high ALC both at baseline and at the EOT showed significantly longer OS than others (p = 0.0201). Similarly, patients with a low NLR both at baseline and at the EOT showed significantly longer OS after EOT than others (p = 0.0136). Multivariable analysis revealed that the NLR at EOT (low vs. high) and changes in NLR (low at baseline to low at EOT vs. others) were significant and independent prognostic factors for OS after EOT (p = 0.0337, p = 0.0039, respectively). CONCLUSION: NLR at EOT with CDK4/6 inhibitors is a significant and independent prognostic marker for patients with ER-positive HER2-negative advanced breast cancer.

Acquired gene alterations in patients treated with ribociclib plus endocrine therapy or endocrine therapy alone using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials.

BACKGROUND: A prior pooled analysis of the MONALEESA-2, -3, and -7 trials identified baseline markers predictive of sensitivity or resistance to ribociclib plus endocrine therapy (ET). We report the results of an analysis of paired baseline and end-of-treatment (EOT) circulating tumor DNA (ctDNA) samples across the MONALEESA trials. PATIENTS AND METHODS: Paired baseline and EOT ctDNA samples from MONALEESA-2, -3, and -7 were sequenced using a targeted next-generation sequencing panel. Genes with an EOT alteration prevalence of >5% were included. A McNemar test was performed on paired samples and adjusted for multiple testing to control the false discovery rate. A Bayesian mixed-effects model was used to adjust for ctDNA fraction at both time points and for study differences. RESULTS: The analysis included 523 paired samples. At EOT, 21 genes had a >5% alteration prevalence. A trend for higher ctDNA fraction at EOT vs baseline (P=0.08) was observed. Prevalence of alterations was higher at EOT vs baseline in RB1, SPEN, TPR, PCDH15, and FGFR2 in the ribociclib arm; PBRM1 in the placebo arm; and ESR1 in both arms. The mixed-effects model demonstrated that the same trends for increased prevalence of these alterations at EOT were observed after adjusting for ctDNA fraction and that the increased rate of RB1 and SPEN alterations at EOT were specific to ribociclib plus ET. Analysis of ESR1 indicated a similar increase at EOT in both arms. The most common acquired ESR1 mutations at EOT included Y537C/N/S/D, D538G, E380Q, and L536H/R/P/LC. The prevalence of PIK3CA hotspot mutations at baseline and EOT was similar. CONCLUSIONS: This analysis identified acquired gene alterations in patients with HR+/HER2- advanced breast cancer treated with ribociclib plus ET or placebo plus ET. These data may support further studies on acquired resistance mechanisms and inform future systemic interventions in the post-CDK4/6 inhibitor setting.

Acute Lymphoblastic Leukemia in a Patient With Advanced Breast Cancer Treated With Cyclin-Dependent Kinase 4/6 Inhibitors and Endocrine Therapy.

This case shares the case of a post-menopausal woman who develops Philadelphia chromosome-positive B cell acute lymphoblastic leukemia (B-ALL) while receiving treatment for invasive ductal carcinoma (IDC) of the breast. The patient received a cyclin-dependent kinase (CDK) 4/6 inhibitor + aromatase inhibitor (AI) for the IDC; hyperfractionate cyclophosphamide, vincristine sulfate, doxorubicin hydrochloride (Adriamycin), methotrexate, and cytarabine (hyperCVAD), and the steroid hormone dexamethasone were added to treat the B-ALL. HyperCVAD combined with CDK 4/6 inhibitor + AI was very well tolerated. The CDK 4/6 inhibitor and AI were only held once in the treatment course due to adverse effect (AE) intolerance. The patient remains on a CDK 4/6 inhibitor and ponatinib with only low-grade fatigue as an AE. This case underscores the importance of a concurrent approach to managing hematologic and breast malignancies. The combined treatment regimens were effective and well-tolerated. Vigilant follow-up is essential for patients in remission from both malignancies, ensuring effective disease surveillance and treatment management. Integrated care remains pivotal for optimal outcomes.

Dose reduction and discontinuation due to the combination of CDK4/6 inhibitors and endocrine drugs: a systematic review and meta-analysis.

BACKGROUND: With the widespread use of CDK4/6 inhibitors, the number of discontinuations and reductions due to adverse events is increasing. Therefore, we examined the risk of dose reduction, discontinuation, and occurrence of serious adverse events and death due to adverse events when CDK4/6 inhibitors are combined with endocrine drugs. METHODS: We searched English-language articles published up to February 10, 2024, using RR values (risk ratio) to indicate the risk of discontinuation, dose reduction, death, and the risk of serious adverse events. RESULTS: When CDK4/6 inhibitors were used in combination with endocrine drugs, abemaciclib resulted in the highest risk of discontinuation, dose reduction, and serious adverse events. Ribociclib caused the highest risk of death. CONCLUSION: When using CDK4/6 inhibitors in the clinical setting, a comprehensive evaluation should be performed to avoid dosage reductions and discontinuations and to choose the most appropriate treatment regimen.