Effect of CDK4/6 Inhibitors on Tumor Immune Microenvironment

Cancer is an abnormal proliferation of cells that is stimulated by cyclin-dependent kinases (CDKs) and defective cell cycle regulation. The essential agent that drive the cell cycle, CDK4/6, would be activated by proliferative signals. Activated CDK4/6 results in the phosphorylation of the neuroblastoma protein (RB) and the release of the transcription factor E2F, which promotes the cell cycle progression. CDK4/6 inhibitor (CDK4/6i) has been currently a research focus, which inhibits the CDK4/6-RB-E2F axis, thereby reducing the cell cycle transition from G1 to S phase and mediating the cell cycle arrest. This action helps achieve an anti-tumor effect. Recent research has demonstrated that CDK4/6i, in addition to contributing to cell cycle arrest, is also essential for the interaction between the tumor cells and the host immune system, i.e., activating the immune system, strengthening the tumor antigen presentation, and reducing the number of regulatory T cells (Treg). Additionally, CDK4/6i would elevate the level of PD-L1, an immunosuppressive factor, in tumor cells, and CDK4/6i in combination with anti-PD-L1 therapy would more effectively reduce the tumor growth. Our results showed that CDK4/6i caused autophagy and senescence in tumor cells. Herein, the impact of CDK4/6i on the immune microenvironment of malignant tumors was mainly focused, as well as their interaction with immune checkpoint inhibitors in affecting anti-tumor immunity.

Neurocognitive impairment in females with breast cancer treated with endocrine therapy and CDK4/6 inhibitors: a pharmacovigilance study using the World Health Organization's database

Importance: Endocrine therapies (ETs) and inhibitors of cyclin-dependent kinases-4/6 (iCDK4/6s) are a standard treatment in breast cancer. However, data on potential neurocognitive impacts remain inconsistent for ET and are scarce for iCDK4/6s. Objective: To evaluate whether ET and iCDK4/6s are associated with neurocognitive impairment (NCI). Methods: We used observational, real-world cases of NCI from the World Health Organization's database VigiBase® to perform disproportionality analysis. Cases were defined as any symptom of NCI in females treated with ETs or iCDK4/6s. The study period was from the date of the first adverse event reported in VigiBase® with iCDK4/6s (1 January 2014) until the date of data extraction (16 March 2022). In our primary analysis, we calculated the reporting odds ratio (ROR) adjusted for age to identify a potential association between NCI and individual ETs in isolation or in combination with iCDK4/6s. We also performed subgroup analyses by the NCI class. Results: We identified 2.582 and 1.943 reports of NCI associated with ETs and iCDK4/6s, respectively. NCI was significantly associated with each ET [anastrozole: n = 405, aROR = 1.52 (95% CI: 1.37-1.67); letrozole: n = 741, aROR = 1.37 (95% CI: 1.27-1.47); exemestane: n = 316, aROR = 1.37 (95% CI: 1.22-1.53); tamoxifen: n = 311, aROR = 1.25 (95% CI: 1.12-1.40); and fulvestrant: n = 319, aROR = 1.19 (95% CI: 1.06-1.33)] and only with palbociclib for iCDK4/6s [n = 1,542, aROR = 1.41 (95% CI: 1.34-1.48)]. Conclusion: These findings suggest that in females treated for breast cancer, all ETs may be associated with NCI. However, amongst iCDK4/6s, NCI may be specific to palbociclib. NCI most frequently involved learning and memory as well as language. Neurocognitive impact of treatments requires better consideration and management.

Real-World Predictors of Severe Neutropenia Associated with Palbociclib and Endocrine Therapy for Metastatic Breast Cancer in Japanese Patients

Therapy for patients of metastatic breast cancer based on palbociclib, a cyclin-dependent kinase 4/6 inhibitor, has been approved in Japan. However, the risk factors for palbociclib-induced severe neutropenia in Japanese patients are rarely reported. Hence, the present study is aimed to identify the risk factors for adverse events requiring palbociclib dose reduction or discontinuation, and to identify the factors necessary to identify a more stable strategy for treatment continuation. This retrospective cohort analysis included patients with advanced breast cancer treated with 125 mg/d palbociclib. We demonstrated that severe neutropenia required significant dose reduction or therapy cessation. Most (77%) of the patients had severe neutropenia within the three courses. Risk factors for grade 3 or higher included low neutrophil counts (< 3250 /µL) before treatment [odds ratio (OR) = 9.10, 95% confidence interval (CI) (2.80-29.41), p < 0.001] and high age-adjusted Charlson comorbidity index (> 9) [OR = 1.64, 95% CI (1.09-2.48), p = 0.018]. Thus, low baseline neutrophil counts and high values for Age-adjusted Charlson comorbidity index are prospective predictive markers for palbociclib-induced severe neutropenia.

Tolerability of palbociclib in younger and older patients with advanced breast cancer

INTRODUCTION

Palbociclib is a small-molecule cyclin-dependent kinase 4/6 inhibitor used to treat hormone receptor-positive, human epidermal growth factor receptor-2 negative advanced breast cancer. Patient-specific factors impacting dose reductions or discontinuations are unknown.

METHODS

The primary objective was to evaluate the association of age (<60 vs. ≥60 years) with palbociclib dose reductions or discontinuations secondary to neutropenia. This single-center, retrospective chart review included hormone receptor-positive, human epidermal growth factor receptor-2 negative advanced breast cancer patients ≥18 years treated with palbociclib between April 2015 and May 2020. Patients <60 years at the time of palbociclib initiation were in the younger group and patients ≥60 years were in the older group.

RESULTS

Among the 107 patients included, younger patients were less likely than older patients to have a palbociclib starting dose <125 mg (0% vs. 11.9%, p = 0.02). Differences in palbociclib dose reductions or treatment discontinuations secondary to neutropenia were not detected (35.4% vs. 42.4%, p = 0.55). Neither the total number of palbociclib dose reductions (none: 54.2% vs. 49.1%, one: 33.3% vs. 42.4%, two: 12.5% vs. 8.5%, p = 0.61), nor the final dose of palbociclib (125 mg: 54.2% vs. 40.7%, 100 mg: 29.2% vs. 27.1%, 75 mg: 16.7% vs. 32.2%, p = 0.17) differed between younger and older patients.

CONCLUSIONS

Age (<60 vs. ≥60 years) was not associated with the rate of palbociclib dose reductions or discontinuations secondary to neutropenia. Older (≥60 years) patients were more likely to start palbociclib at lower doses which may impact neutropenia and non-neutropenic intolerance.

Determination and clinical significance of bone pseudoprogression in hormone receptor-positive metastatic breast cancer

Background

^99mTechnetium labeled methylene diphosphonate bone scans (BSs) are commonly used to monitor disease progression in bone for patients with metastatic breast cancer (MBC). However, new BS lesions may represent osteoblastic bone healing, which we now define as bone pseudoprogression. In this study, we aimed to assess the clinical significance and determination methods of bone pseudoprogression.

Methods

This retrospective analysis was conducted among 48 patients with hormone receptor-positive MBC treated with first-line endocrine therapy. Four months after initiating therapy, all the participants did not show extraosseous disease progression. Participants were divided into two groups according to the presence of new BS lesions. All the patients continued on treatment until explicit disease progression (extraosseous disease progression or progressive lysis on bone lesions). Explicit progression-free survival (PFS) and extraosseous objective response rate were analyzed between the two groups.

Results

New BS lesions were observed in 11 of 48 (22.9%) patients. All the new BS lesions appeared as osteoblastic bone lesions on computed tomography. For patients with new BS lesions, the median PFS was 26.57 months [95% confidence interval (CI) 15.46-37.68], which was similar to that (29.57 months; 95% CI 19.24-39.90) in patients without new BS lesions [hazard ratio: 1.098 (95% CI 0.482-2.503), p = 0.818]. Notably, 82.9% of patients without new BS lesions showed an extraosseous objective response, whereas 85.7% of patients with new BS lesions demonstrated an extraosseous objective response [odds ratio: 0.806 (95% CI 0.061-5.682), p = 0.999]. The median interval between bone pseudoprogression and true disease progression was 21.26 months (95% CI 10.11-32.42).

Conclusions

Osteoblastic new BS lesions detected on follow-up BSs may represent bone pseudoprogression. Clinicians should raise awareness of bone pseudoprogression, thereby avoiding premature discontinuation of therapy and maximizing the opportunity to benefit from endocrine therapy. Due to the small sample size and retrospective nature of the study, large prospective clinical trials are needed to confirm our findings.