Abstract
BACKGROUND: Breast cancer is the most common type of cancer among women worldwide. Hormone receptor-positive (HR(+)), human epidermal growth factor receptor 2-negative (HER2(-)) breast cancer constitutes the predominant subtype, accounting for approximately 70% of all breast cancer cases. Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, in conjunction with endocrine therapy (ET), have been used as the standard treatment for patients diagnosed with HR(+) advanced breast cancer. The hematological adverse effects associated with CDK4/6 inhibitors include leukopenia, neutropenia, anemia, and thrombocytopenia, but the incidence of hematological malignancies following treatment with these agents remains relatively rare. CASE DESCRIPTION: In this study, we present a case of a 71-year-old woman who was diagnosed with metastatic breast cancer and subsequently developed chronic myeloid leukemia (CML) following her treatment regimen with palbociclib and exemestane. In response to this new diagnosis, the patient commenced therapy with imatinib mesylate while discontinuing palbociclib and receiving exemestane alone for breast cancer. After three months of diligent therapy with imatinib, chronic myeloid leukemia was effectively managed, which permitted the reintroduction of palbociclib at a reduced dosage. CONCLUSIONS: This case underscores the pressing need for further research to enhance our understanding of the adverse events associated with treatment using CDK4/6 inhibitors, particularly concerning their effects on the hematological system. Additionally, it highlights the significance of long-term monitoring in clinical practice for patients receiving therapy with CDK4/6 inhibitors.