Predictors for development of palbociclib-induced neutropenia in breast cancer patients as determined by ordered logistic regression analysis

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.

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

The impact of body mass index (BMI) on treatment outcomes in patients with cancer is gaining increasing attention given the limited data available. The aim of this study was to investigate the contribution of BMI on the safety and efficacy profile of palbociclib in 134 patients with metastatic luminal-like breast cancer treated with palbociclib and endocrine therapy (ET). Normal-weight and underweight patients (BMI<25) were compared with overweight and obese (BMI≥25). Detailed clinical and demographic data were collected. Patients with a BMI<25 had a higher incidence of relevant-hematologic toxicities (p = 0.001), dose reduction events (p = 0.003), and tolerated lower dose intensities (p = 0.023) compared to patients with a BMI≥25. In addition, patients with a BMI<25 had significantly shorter progression-free survival (log-rank p = 0.0332). A significant difference was observed in the subgroup of patients for whom systemic palbociclib concentrations were available: patients with a BMI<25 had a 25% higher median minimum plasma concentrations (C_min) compared to BMI≥25. This study provides compelling evidence for a clinically relevant contribution of BMI in discriminating a group of patients who experienced multiple toxicities that appeared to affect treatment adherence and lead to poorer survival. BMI could become a valuable tool for personalizing the starting dose of palbociclib to improve its safety and efficacy.

Risk Factors for Palbociclib-Induced Early Developing Neutropenia in Patients with Hormone Receptor-Positive Metastatic Breast Cancer

PURPOSE

This study aimed to determine the risk factors for palbociclib-induced grade 4 or grade 3 neutropenia (NP) requiring dose reduction or delayed treatment in patients with HR+/HER2-metastatic breast cancer in the first 3 cycles (early grade 3/4 NP) and whether the early developing grade 3/4 NP affects progression-free survival.

METHODS

A retrospective study using electronic medical records was conducted on patients who received palbociclib for metastatic breast cancer between January 2018 and August 2022. The early grade 3/4 NP risk factors were evaluated with univariate and multivariable logistic regression analyses. In addition, the Kaplan-Meier method was used to estimate the median progression-free survival (PFS) to analyze the effect of early grade 3/4 NP on treatment.

RESULTS

Out of the 264 patients included in this study, 173 (65.6%) experienced early grade 3/4 NP. A total of four models were applied for multivariable analysis to identify early grade 3/4 NP-developing factors. Low baseline ANC, WBC, PLT, and BSA were significant risk factors for early grade 3/4 NP; baseline ANC < 3700/mm³, WBC < 6.30 × 10⁹/mm³, PLT < 230 × 10⁹/mm³, and BSA < 1.58 m² increased the risk by approximately 4.0-fold, 3.7-4.0-fold, 2.1-fold, and 2.0-fold, respectively. Early grade 3/4 NP did not affect PFS (p = 0.710), although patients with early grade 3/4 NP had more frequent dose reductions or treatment delays.

CONCLUSIONS

Based on the results, low baseline ANC, WBC, PLT, and BSA were associated with early grade 3/4 NP. Patients with risk factors require careful monitoring, and this study is expected to help predict NP, which may appear in early treatment.

Investigation on acquired palbociclib resistance by LC-MS based multi-omics analysis

Palbociclib is a specific CDK4/6 inhibitor that has been widely applied in multiple types of tumors. Different from cytotoxic drugs, the anticancer mechanism of palbociclib mainly depends on cell cycle inhibition. Therefore, the resistance mechanism is different. For clinical cancer patients, drug resistance is inevitable for almost all cancer therapies including palbociclib. We have trained palbociclib resistant cells in vitro to simulate the clinical situation and applied LC-MS multi-omics analysis methods including proteomic, metabolomic, and glycoproteomic techniques, to deeply understand the underly mechanism behind the resistance. As a result of proteomic analysis, the resistant cells were found to rely on altered metabolic pathways to keep proliferation. Metabolic processes related to carbohydrates, lipids, DNA, cellular proteins, glucose, and amino acids were observed to be upregulated. Most dramatically, the protein expressions of COX-1 and NDUFB8 have been detected to be significantly overexpressed by proteomic analysis. When a COX-1 inhibitor was hired to combine with palbociclib, a synergistic effect could be obtained, suggesting the altered COX-1 involved metabolic pathway is an important reason for the acquired palbociclib resistance. The KEGG pathway of N-glycan biosynthesis was identified through metabolomics analysis. N-glycoproteomic analysis was therefore included and the global glycosylation was found to be elevated in the palbociclib-resistant cells. Moreover, integration analysis of glycoproteomic data allowed us to detect a lot more proteins that have been glycosylated with low abundances, these proteins were considered to be overwhelmed by those highly abundant proteins during regular proteomic LC-MS detection. These low-abundant proteins are mainly involved in the cellular biology processes of cell migration, the regulation of chemotaxis, as well as the glycoprotein metabolic process which offered us great more details on the roles played by N-glycosylation in drug resistance. Our result also verified that N-glycosylation inhibitors could enhance the cell growth inhibition of palbociclib in resistant cells. The high efficiency of the integrated multi-omics analysis workflow in discovering drug resistance mechanisms paves a new way for drug development. With a clear understanding of the resistance mechanism, new drug targets and drug combinations could be designed to resensitize the resistant tumors.

Targeted therapy for breast cancer: An overview of drug classes and outcomes

The last 25 years have seen significant growth in new therapeutic options for breast cancer, termed targeted therapies based on their ability to block specific pathways known to drive breast tumor growth and survival. Introduction of these drugs has been made possible through advances in the understanding of breast cancer biology. While the promise of targeted therapy for breast cancer has been clear for some time, the experience of the clinical use of multiple drugs and drug classes allows us to now present a summary and perspective as to the success and impact of this endeavor. Here we will review breast cancer targeted therapeutics in clinical use. We will provide the rationale for their indications and summarize clinical data in patients with different breast cancer subtypes, their impact on breast cancer progression and survival and their major adverse effects. The focus of this review will be on the development that has occurred within classes of targeted therapies and subsequent impact on breast cancer patient outcomes. We will conclude with a perspective on the role of targeted therapy in breast cancer treatment and highlight future areas of development.

Pharmacokinetic Variability Drives Palbociclib-Induced Neutropenia in Metastatic Breast Cancer Patients: Drug-Drug Interactions Are the Usual Suspects

Palbociclib is a good candidate for therapeutic drug monitoring (TDM) due to its narrow therapeutic range and frequency of toxicities, particularly high-grade neutropenia. In this prospective, bicentric clinical trial, we evaluated the palbociclib exposure−toxicity relationship and determined the relevant sources of palbociclib pharmacokinetic variability, including drug−drug interactions (DDI). We followed 58 patients (mean age: 62.9 years) for 1 year. The geometric median of palbociclib plasma trough concentration (Ctrough) was 74.1 ng/mL. Neutropenia occurred in 70.7% of patients (high grade in 67.2% of patients). High-grade neutropenia occurrence during the first two palbociclib cycles was higher in patients with lower neutrophil count at initiation (p = 0.002). Palbociclib plasma Ctrough was correlated with high-grade neutropenia occurrence during the first two cycles (p = 0.024, OR 5.51). Co-treatment with agents that may interfere with palbociclib PK significantly influenced palbociclib Ctrough (p < 0.05). CYP3A4/P-glycoprotein inhibitors increased by 25% palbociclib Ctrough (p = 0.035), while antacids reduced it by 20% (p = 0.036). However, DDI did not have any significant effect on high-grade neutropenia occurrence (p > 0.05). This study confirms the major role of TDM to manage palbociclib safe use from the first week of treatment, particularly the significant incidence of hematological toxicity. Moreover, this first dedicated prospective study confirmed the importance of characterizing co-treatments to limit the DDI risk with oral-targeted therapies.