Clinical impact of body mass index on palbociclib treatment outcomes and effect on exposure

Drug-Drug interactions and special considerations in breast cancer patients treated with CDK4/6 inhibitors: A comprehensive review

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) have reshaped the treatment paradigm of hormone receptor positive (HR + )/HER2-negative breast cancer in both adjuvant and metastatic settings. However, their metabolism via the cytochrome P450 (CYP3A4) pathway poses a high risk of clinically relevant drug-drug interactions (DDIs), requiring vigilant therapeutic strategies. This review provides a comprehensive analysis of the pharmacokinetics, metabolism, and interaction profiles of palbociclib, ribociclib, and abemaciclib, emphasizing their differential DDI risks. Among these agents, ribociclib has been associated with a higher risk of QTc prolongation and CYP3A4-mediated interactions in some studies, whereas abemaciclib demonstrates a relatively favorable DDI profile. However, data remain limited and are largely derived from indirect comparisons or pharmacovigilance analyses. We further examine the clinical implications of drug-drug interactions with frequently co-prescribed agents, including proton pump inhibitors, antifungal medications, anticoagulants, and lipid-lowering therapies. Practical recommendations regarding drug selection, therapeutic drug monitoring, and dose adjustment are discussed with attention to the individual characteristics of each CDK4/6i. Dose modifications and monitoring in patients with renal or hepatic impairment are also discussed. Emerging pharmacogenomic data suggest that genetic polymorphisms in CYP3A4 and ABCG2 influence drug exposure and toxicity, reinforcing the need for personalized treatment approaches. As the use of CDK4/6i expands across different breast cancer settings, addressing DDIs through precision medicine strategies such as pharmacogenomic profiling, physiologically based pharmacokinetic modeling, and artificial intelligence-guided clinical support will be essential to personalize therapy and optimize safety.

Body mass index and clinical outcomes in breast cancer patients undergoing endocrine therapy: A meta-analysis and Mendelian randomization study

OBJECTIVE

The relationship between breast cancer prognosis, Body Mass Index (BMI), and endocrine therapy outcomes remains inconclusive. This study examines BMI's impact on survival outcomes in breast cancer patients receiving endocrine therapy through Mendelian randomization (MR) and a comprehensive clinical data review.

METHODS

A meta-analysis of clinical studies up to January 2024 investigated the association between obesity and the efficacy and safety of endocrine therapy. Additionally, a two-sample MR approach using genetic variants evaluated the causal effect of BMI on survival in breast cancer patients undergoing endocrine therapy.

RESULTS

Meta-analysis of eight studies (n = 12,673) found that BMI generally does not affect therapy outcomes. However, subgroup analysis showed that overweight patients on anastrozole had shorter disease-free survival (DFS) than normal-weight patients (Hazard Ratio (HR) = 1.21, P = 0.03), increased fatigue (Risk Ratio (RR) = 0.91, P = 0.03), and higher nausea with cyclin-dependent kinase 4/6(CDK4/6)inhibitors (Risk Ratio, RR = 0.69, P < 0.0001). Normal-weight patients on tamoxifen had a greater risk of bone pain (RR = 1.25, P = 0.03). Further MR analysis revealed no causal link between BMI and 5-year or 15-year survival rates in endocrine-treated patients (5-year HR = 0.7923, 95 % Confidence Interval (CI)[0.2053, 3.0581], P = 0.7355; 15-year HR = 0.9793, 95 % CI [0.7121, 1.3469], P = 0.898).

CONCLUSION

Current meta-analysis and MR findings suggest no significant link between BMI and the overall efficacy of endocrine therapy in breast cancer. However, BMI should be considered in anastrozole therapy due to differential effects on DFS and adverse events.

Identification and Management of Medical Comorbidities in Patients With HR+/HER2- Metastatic Breast Cancer Treated With CDK4/6 Inhibitors: Literature Review and Recommendations From Experts in Spain Opinion

Approximately one-third of patients with breast cancer have comorbidities at the time of their diagnosis. Recommendations for managing metastatic breast cancer are usually based on the results of clinical trials, which often limit patients with comorbidities. However, comorbidities greatly influence the quality of life, patient survival rate and treatment choice, particularly in older patients. The objective of this review was to identify clinically relevant comorbidities in patients with metastatic breast cancer, analyze the clinical approach to the treatment of these comorbidities, and propose recommendations from experts. An expert panel of eight medical oncologists identified seven therapeutic areas associated with the most relevant comorbidities in metastatic breast cancer: cardiovascular, gastrointestinal, endocrine/metabolic, renal, geriatric, psychological, and pain related. A clinical specialist from each therapeutic area specific to the relevant comorbidities (n = 8) joined the panel of experts (n = 8) to provide guidance on the appropriate management of these comorbidities. The specific comorbidities analyzed were hypertension, atrial fibrillation, venous thromboembolism, obesity, diabetes mellitus, cancer cachexia, chronic kidney disease, age-related disorders, arthritis, and fibromyalgia. In most cases, patients with metastatic breast cancer and medical comorbidities are polymedicated and/or vulnerable to toxicity. The oncologists provided recommendations on initial assessment and monitoring, follow-up recommendations, and warning signs and symptoms for referral to corresponding specialists based on their experience. The panel of experts also explored clinical scenarios related to each comorbidity and recommended a preferred CDK4/6 inhibitor based on available evidence regarding drug-drug interactions and potential for toxicity.

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

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

Efficacy and Safety of Cyclin-Dependent Kinase 4/6 Inhibitors in Patients with Breast Cancer: A Systematic Review and Meta-analysis of Randomized Controlled Trials and Real-World Studies

BACKGROUND

The efficacy and safety of cyclin-dependent kinase (CDK)4/6 inhibitors in patients with breast cancer have been investigated by large-scale trials sponsored by drug companies. A lack of real-world evidence may lead to biases.

OBJECTIVE

We systematically reviewed the large-scale clinical trials and real-world data to investigate the efficacy and safety of CDK4/6 inhibitors in patients with breast cancer.

PATIENTS AND METHODS

We searched PubMed, Embase, and Cochrane Library from the inception of each database to January 2024. We included both prospective and retrospective studies reporting the survival outcomes or adverse effects of CDK4/6 inhibitors in patients with breast cancer.

RESULTS

We included 41 prospective trials and 80 retrospective studies involving a total of 69,535 patients. Our meta-analysis of double-arm studies revealed that all types of CDK4/6 inhibitors significantly improved overall survival and progression-free survival. The pooled estimates of the 1-year overall survival (OS) rates and 1-year progression-free survival (PFS) rates in single-arm real-world studies were 74.8% and 49.4% for abemaciclib, 84.1% and 55.7% for palbociclib, and 93.4% and 62.2% for ribobiclib, respectively. In terms of adverse effects, Asian patients were significantly more likely to experience neutropenia and increased alanine aminotransferase, whereas Western patients were significantly more likely to have grade 3 or 4 adverse effects and constipation.

CONCLUSIONS

CDK4/6 inhibitors can improve OS and PFS in patients with advanced breast cancer. The incidence of adverse effects may differ with drugs and with ethnicity. On the basis of our findings, clinicians can select suitable CDK4/6 inhibitors for patients by conducting thorough clinical evaluations.

Timing of Dose Reductions and Survival Outcomes in Metastatic Breast Cancer Patients Treated with Cyclin-Dependent Kinase 4/6 Inhibitors

BACKGROUND/OBJECTIVES

Dose reductions in CDK4/6 inhibitors, such as ribociclib and palbociclib, are often necessary due to treatment-related toxicities in patients with advanced breast cancer. This study aims to evaluate the impact of the timing of dose reductions on progression-free survival (PFS) and overall survival (OS) in a real-world cohort.

METHODS

This single-center, retrospective study included patients treated with ribociclib or palbociclib between 2019 and 2023 at a cancer center in Turkey. Dose reductions due to drug-related toxicities were recorded, and survival outcomes were analyzed. Patients were categorized based on the timing of dose reductions: within the first 3 months (early) and after 3 months (late).

RESULTS

Among 392 patients (mean age 57.13 years), 16.8% had dose reductions within 3 months, 21.7% had late dose reductions, and 61.5% had no dose reductions. The mPFS was 14.26 months for early dose reductions, 33.12 months for late dose reductions, and 20.6 months for no dose reductions (p < 0.001). The mOS was 37.12 months for early dose reductions, not reached for late dose reductions, and 57.76 months for no dose reductions (p < 0.001). Hematological toxicity, primarily neutropenia, was the most common cause of dose reductions. The ECOG performance status, line of therapy, and CDK4/6 inhibitor type were also significant predictors of PFS and OS.

CONCLUSIONS

Early dose reductions in CDK4/6 inhibitors negatively affect PFS and OS, highlighting the importance of maintaining treatment intensity in the first 3 months. However, late dose reductions do not negatively affect progression-free survival (PFS) or overall survival (OS), with late dose reductions associated with better outcomes. Prospective studies in larger patient populations will further clarify our knowledge on this subject.

Predictors of abemaciclib discontinuation in patients with breast cancer: a multicenter retrospective cohort study

OBJECTIVE

This study explored the predictors of abemaciclib discontinuation, a cyclin-dependent kinase 4 and 6 inhibitor, in patients with breast cancer.

MATERIAL AND METHODS

Between November 2018 and March 2023, 147 patients with breast cancer treated with abemaciclib at Osaka Medical and Pharmaceutical University Hospital and Kindai University Nara Hospital were included. The exclusion criteria were as follows: lack of blood testing within 2 weeks prior to starting abemaciclib therapy, transfer to another facility after the commencement of abemaciclib therapy, and discontinuation of abemaciclib therapy due to the diagnosis of another cancer. The duration from the initiation of abemaciclib to discontinuation for any reason and to temporary suspension or dose reduction due to adverse events were analyzed as outcome variables using multivariate Cox regression analysis.

RESULTS

Baseline weight < 54 kg, bone metastases, and hemoglobin level ≤ 12.4 g/dL were independent predictors of abemaciclib discontinuation for any reason. The main adverse events leading to abemaciclib discontinuation were liver enzyme elevation and gastrointestinal symptoms. Additionally, focusing on the adverse event of abemaciclib, a baseline weight < 54 kg was an independent predictor of temporary suspension or dose reduction due to adverse events. The most common adverse events leading to temporary suspension or dose reduction were neutropenia and diarrhea.

CONCLUSION

Patients with lower body weight are more susceptible to the adverse events of abemaciclib, increasing their risk of treatment discontinuation. In such patients, strict monitoring of adverse events and consideration of more frequent medical visits are necessary from the start of abemaciclib therapy.

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.

High BMI Is Associated with Changes in Peritumor Breast Adipose Tissue That Increase the Invasive Activity of Triple-Negative Breast Cancer Cells

Breast cancer is the most common cancer in women with multiple risk factors including smoking, genetics, environmental factors, and obesity. Smoking and obesity are the top two risk factors for the development of breast cancer. The effect of obesity on adipose tissue mediates the pathogenesis of breast cancer in the context of obesity. Triple-negative breast cancer (TNBC) is a breast cancer subtype within which the cells lack estrogen, progesterone, and HER2 receptors. TNBC is the deadliest breast cancer subtype. The 5-year survival rates for patients with TNBC are 8-16% lower than the 5-year survival rates for patients with estrogen-receptor-positive breast tumors. In addition, TNBC patients have early relapse rates (3-5 years after diagnosis). Obesity is associated with an increased risk for TNBC, larger TNBC tumors, and increased breast cancer metastasis compared with lean women. Thus, novel therapeutic approaches are warranted to treat TNBC in the context of obesity. In this paper, we show that peritumor breast adipose-derived secretome (ADS) from patients with a high (>30) BMI is a stronger inducer of TNBC cell invasiveness and JAG1 expression than peritumor breast ADS from patients with low (<30) BMI. These findings indicate that patient BMI-associated changes in peritumor AT induce changes in peritumor ADS, which in turn acts on TNBC cells to stimulate JAG1 expression and cancer cell invasiveness.

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.

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.

Exploring pharmacokinetic variability of palbociclib in HR+/HER2- metastatic breast cancer: a focus on age, renal function, and drug-gene interactions

Palbociclib, an oral inhibitor of cyclin-dependent kinase 4 and 6, is approved for the treatment of metastatic breast cancer. This study investigated the influence of diverse clinical and biological factors-age, renal function, genetic variations, and concomitant medications (pharmacokinetic covariates)-on palbociclib pharmacokinetics. Employing a validated LC-MS/MS method, we analyzed the minimum plasma concentrations (Ctrough) of palbociclib in 68 women and determined the percentage deviations from the median Ctrough for each dosage group. Variations in a panel of absorption, distribution, metabolism, and excretion (ADME) genes were assessed using end-point allele-specific fluorescence detection and pyrosequencing. Two distinct patient cohorts were defined based on median values of age, creatinine, and eGFR, which exhibited statistically significant differences in percentage deviations (p = 0.0095, p = 0.0288, and p = 0.0005, respectively). Homozygous carriers of the PPARA variants displayed larger positive percentage deviations than the other group (p = 0.0292). Similarly, patients concurrently taking CYP3A and P-glycoprotein inhibitors alongside anticancer therapy exhibited significant variations (p = 0.0285 and p = 0.0334, respectively). Furthermore, exploring the drug-drug-gene interactions between inhibitors of CYP3A and P-glycoprotein with their respective genetic variants revealed two patient groups with statistically different percentage deviations (p = 0.0075, p = 0.0012, and p = 0.0191, respectively). These results could help address cases where pharmacokinetic covariates or subclinical conditions impair palbociclib adherence or response, aiming to offer tailored dosing strategies or monitoring for individual patients.

Reasons for non-feasibility of therapeutic drug monitoring of oral targeted therapies in oncology - an analysis of the closed cohorts of a multicentre prospective study

BACKGROUND

Therapeutic drug monitoring (TDM) - performing dose adjustments based on measured drug levels and established pharmacokinetic (PK) targets - could optimise treatment with drugs that show large interpatient variability in exposure. We evaluated the feasibility of TDM for multiple oral targeted therapies. Here we report on drugs for which routine TDM is not feasible.

METHODS

We evaluated drug cohorts from the Dutch Pharmacology Oncology Group - TDM study. Based on PK levels taken at pre-specified time points, PK-guided interventions were performed. Feasibility of TDM was evaluated, and based on the success and practicability of TDM, cohorts could be closed.

RESULTS

For 10 out of 24 cohorts TDM was not feasible and inclusion was closed. A high incidence of adverse events resulted in closing the cabozantinib, dabrafenib/trametinib, everolimus, regorafenib and vismodegib cohort. The enzalutamide and erlotinib cohorts were closed because almost all PK levels were above target. Other, non-pharmacological reasons led to closing the palbociclib, olaparib and tamoxifen cohort.

CONCLUSIONS

Although TDM could help personalising treatment for many drugs, the above-mentioned reasons can influence its feasibility, usefulness and clinical applicability. Therefore, routine TDM is not advised for cabozantinib, dabrafenib/trametinib, enzalutamide, erlotinib, everolimus, regorafenib and vismodegib. Nonetheless, TDM remains valuable for individual clinical decisions.

Therapeutic Monitoring of Palbociclib, Ribociclib, Abemaciclib, M2, M20, and Letrozole in Human Plasma: A Novel LC-MS/MS Method

BACKGROUND

Therapeutic drug monitoring (TDM) using cyclin-dependent kinase inhibitors (CDK4/6is) is a novel approach for optimizing treatment outcomes. Currently, palbociclib, ribociclib, and abemaciclib are the available CDK4/6is and are primarily coadministered with letrozole. This study aimed to develop and validate an LC-MS/MS method for the simultaneous analysis of CDK4/6is, 2 active metabolites of abemaciclib (M2 and M20), and letrozole in human plasma for use in TDM studies.

METHODS

Sample pretreatment comprised protein precipitation with methanol and dilution of the supernatant with an aqueous mobile phase. Chromatographic separation was achieved using a reversed-phase XBridge BEH C18 column (2.5 μm, 3.0 × 75 mm XP), with methanol serving as the organic mobile phase and pyrrolidine-pyrrolidinium formate (0.005:0.005 mol/L) buffer (pH 11.3) as the aqueous mobile phase. A triple quadrupole mass spectrometer was used for the detection, with the ESI source switched from negative to positive ionization mode and the acquisition performed in multiple reaction monitoring mode.

RESULTS

The complete validation procedure was successfully performed in accordance with the latest regulatory guidelines. The following analytical ranges (ng/mL) were established for the tested compounds: 6-300, palbociclib and letrozole; 120-6000, ribociclib; 40-800, abemaciclib; and 20-400, M2 and M20. All results met the acceptance criteria for linearity, accuracy, precision, selectivity, sensitivity, matrix effects, and carryover. A total of 85 patient samples were analyzed, and all measured concentrations were within the validated ranges. The percent difference for the reanalyzed samples ranged from -11.2% to 7.0%.

CONCLUSIONS

A simple and robust LC-MS/MS method was successfully validated for the simultaneous quantification of CDK4/6is, M2, M20, and letrozole in human plasma. The assay was found to be suitable for measuring steady-state trough concentrations of the analytes in patient samples.

Is ctDNA ready to outpace imaging in monitoring early and advanced breast cancer?

INTRODUCTION

Circulating tumor DNA (ctDNA) and radiological imaging are increasingly recognized as crucial elements in breast cancer management. While radiology remains the cornerstone for screening and monitoring, ctDNA holds distinctive advantages in anticipating diagnosis, recurrence, or progression, providing concurrent biological insights complementary to imaging results.

AREAS COVERED

This review delves into the current evidence on the synergistic relationship between ctDNA and imaging in breast cancer. It presents data on the clinical validity and utility of ctDNA in both early and advanced settings, providing insights into emerging liquid biopsy techniques like epigenetics and fragmentomics. Simultaneously, it explores the present and future landscape of imaging methodologies, particularly focusing on radiomics.

EXPERT OPINION

Numerous are the current technical, strategic, and economic challenges preventing the clinical integration of ctDNA analysis in the breast cancer monitoring. Understanding these complexities and devising targeted strategies is pivotal to effectively embedding this methodology into personalized patient care.

Abemaciclib pharmacology and interactions in the treatment of HR+/HER2- breast cancer: a critical review

Abemaciclib (ABE) in combination with endocrine therapy represents the mainstay treatment for either endocrine-resistant metastatic or high-risk early-stage HR+/HER2- breast cancer patients. Hence, an adequate knowledge of this agent pharmacodynamic, pharmacokinetic, and of its drug-drug interactions (DDIs) is crucial for an optimal patients management. Additionally, ABE interference with food and complementary/alternative medicines should be taken into account in the clinical practice. Several online tools allow to freely check DDIs and can be easily consulted before prescribing ABE. According to one of this instruments, ABE display the lowest number of interactions among the available cyclin-dependent kinase 4/6 inhibitors. Still, clinicians should be aware that online tools cannot replace the technical datasheet of the drug as well as a comprehensive clinical assessment for each patient. Here we critically review the main pharmacological features of ABE, then focusing on its potential interactions with drugs, food, and alternative medicine, in order to provide a guide for its optimal use in the treatment of HR+/HER2- breast cancer patients.

Predicting drug-drug interactions in breast cancer patients treated with CDK4/6 inhibitors and forward planning

INTRODUCTION

Cyclin-dependent kinase (CDK) 4/6 inhibitors are cornerstones in the treatment of Hormone Receptor (HR) positive and Human Epidermal Growth factor (HER2) negative metastatic breast cancer. Given their widespread use in the metastatic setting and emerging use in the adjuvant setting, studying drug-drug interactions (DDI) of these medications is of utmost importance.

AREAS COVERED

This review provides key background information on the CDK4/6 inhibitors, palbociclib, ribociclib, and abemaciclib. We discuss drug-drug interactions including those with proton pump inhibitors as well as CYP3A substrates, inhibitors, and inducers. We describe the effect of these drugs on membrane transporters and their substrates as well as those drugs that increase risk of CDK4/6 toxicities. Finally, we explore future directions for strategies to minimize drug-drug interactions.

EXPERT OPINION

It is crucial to be mindful of medications that may interfere with drug absorption, such as proton pump inhibitors, as well as those that interfere with drug metabolism, such as CYP3A4 inhibitors and inducers. Additionally, special consideration should be given to populations at higher risk for polypharmacy, such as older patients with greater comorbidities. These interactions and patient characteristics should be considered when developing individual treatment plans with CDK4/6 inhibitors.

Peripheral blood lymphocytes predict clinical outcomes in hormone receptor-positive HER2-negative advanced breast cancer patients treated with CDK4/6 inhibitors

Background

Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6i) combined with Endocrine Therapy (ET) are the standard treatment for patients with Hormone Receptor-positive/HER2-negative advanced breast cancer (HR+/HER2- aBC).

Objectives

While CDK4/6i are known to reduce several peripheral blood cells, such as neutrophils, lymphocytes and platelets, the impact of these modulations on clinical outcomes is unknown.

Design

A multicenter, retrospective-prospective Italian study.

Methods

We investigated the association between baseline peripheral blood cells, or their early modifications (i.e. 2 weeks after treatment initiation), and the progression-free survival (PFS) of HR+/HER2- aBC patients treated with ETs plus CDK4/6i. Random Forest models were used to select covariates associated with patient PFS among a large list of patient- and tumor-related variables.

Results

We evaluated 638 HR+/HER2- aBC patients treated with ET plus CDK4/6i at six Italian Institutions between January 2017 and May 2021. High baseline lymphocyte counts were independently associated with longer PFS [median PFS (mPFS) 20.1 versus 13.2 months in high versus low lymphocyte patients, respectively; adjusted Hazard Ratio (aHR): 0.78; 95% confidence interval (CI): 0.66-0.92; p = 0.0144]. Moreover, patients experiencing a lower early reduction of lymphocyte counts had significantly longer PFS when compared to patients undergoing higher lymphocyte decrease (mPFS 18.1 versus 14.5 months; aHR: 0.82; 95% CI: 0.73-0.93; p = 0.0037). Patients with high baseline lymphocytes and undergoing a lower reduction, or even an increase, of lymphocyte counts during CDK4/6i therapy experienced the longest PFS, while patients with lower baseline lymphocytes and undergoing a higher decrease of lymphocytes had the lowest PFS (mPFS 21.4 versus 11 months, respectively).

Conclusion

Baseline and on-treatment modifications of peripheral blood lymphocytes have independent prognostic value in HR+/HER2- aBC patients. This study supports the implementation of clinical strategies to boost antitumor immunity in patients with HR+/HER2- aBC treated with ETs plus CDK4/6i.

CDK4/6 inhibitors in the treatment of metastatic breast cancer: Focus on toxicity and safety

The development of oral cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, including palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for patients with hormone-receptor-positive (HR+) and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (BC). When combined with an aromatase inhibitor or fulvestrant, these agents have been approved as first-line therapy in the metastatic setting. Abemaciclib has also gained FDA approval for patients with HR-positive, HER2-negative, node-positive, early BC at high risk of recurrence. Moreover, ribociclib has recently improved disease-free survival in patients with stage II or III HR+/HER2-negative early BC. CDK4/6 inhibitors have favorable safety profiles. However, the available agents have different toxicity profiles that must be clearly discussed with the patients for optimal clinical decisions. This manuscript aims to review CDK4/6 inhibitor-related treatment-associated adverse events, identify risk factors for intolerable adverse events, and assess their safety in special patient populations such as the elderly and those with renal insufficiency. Enhanced knowledge and understanding of CDK4/6 inhibitor-related toxicities can improve treatment strategies and ultimately enhance patient care.

Association of ADME gene polymorphisms on toxicity to CDK4/6 inhibitors in patients with HR+ HER2- metastatic breast cancer

A wide interindividual variability in therapeutic response to cyclin-dependent kinases 4 and 6 inhibitors (CDKis) palbociclib, ribociclib and abemaciclib, among patients with HR+/HER2- metastatic breast cancer has been reported. This study explored the impact of genetic polymorphisms in ADME genes (responsible for drug absorption, distribution, metabolism, and elimination) on CDKis safety profiles in 230 patients. Selected endpoints include grade 3/4 neutropenia at day 14 of the first treatment cycle, early dose-limiting toxicities (DLTs), and dose reductions within the initial three cycles. Our analysis revealed associations between these endpoints and polymorphisms in CYP3A4, CYP3A5, ABCB1, and ABCG2 genes. Their impact on CDKis plasma concentrations (Ctrough) was also examined. Specifically, ABCB1 c.1236C>T and c.2677C>T polymorphisms correlated significantly with grade 3/4 neutropenia at day 14 (OR 3.94, 95% CI 1.32-11.75; p = 0.014 and OR 3.32, 95% CI 1.12-9.85; p = 0.030). Additionally, ABCB1 c.3435C>T was associated with an elevated risk of early DLTs and dose reductions (OR 3.28, 95% CI 1.22-8.84, p = 0.019; OR 2.60, 95% CI 1.20-5.60, p = 0.015). Carriers of the CYP3A4*22 allele also demonstrated in univariate a higher risk of early DLTs (OR 3.10, 95% CI 1.01-9.56, p = 0.049). Furthermore, individuals with the ABCB1 1236T-3435T-2677T(A) variant haplotype exhibited significant associations with grade 3/4 neutropenia at day 14 (OR 3.36, 95% CI 1.20-9.41; p = 0.021) and early DLTs in univariate (OR 3.08, 95% CI 1.19-7.95; p = 0.020). Homozygous carriers of the ABCB1 T-T-T(A) haplotype tended to have a higher mean ribociclib Ctrough (934.0 ng/mL vs. 752.0 ng/mL and 668.0 ng/mL). Regardless preliminary, these findings offer promising insights into the role of pharmacogenetic markers in CDKis safety profiles, potentially contributing to address the interindividual variability in CDKis responses.