Premenopausal Patients With Clinically Aggressive Metastatic Breast Cancer Successfully Treated With a First‐Line Palbociclib‐Containing Regimen: Two Cases and Literature Review

Background Palbociclib, which is an oral small‐molecule cyclin‐dependent kinase 4 and 6 (CDK4/6) inhibitor, demonstrated its efficacy in hormone receptor‐positive (HR+) and human epidermal growth factor receptor 2‐negative (HER2−) metastatic breast cancer together with endocrine therapy. However, patients with visceral crises (symptomatic visceral dissemination) are recommended to consider chemotherapy rather than endocrine‐based therapy. Currently, more reports and evidence support that patients with aggressive visceral metastasis can be effectively managed using both a CDK4/6 inhibitor and endocrine therapy. Case We report two premenopausal patients with HR+/HER2− metastatic breast cancer, whose diseases diffusely involved major organs and were successfully managed with palbociclib and endocrine therapies as the initial therapy. Conclusion In the two cases we reported, first‐line palbociclib therapy shows adequate and timely responses for premenopausal HR+/HER2− metastatic breast cancer patients. Although not widely utilized, frontline therapy with palbociclib combined with endocrine treatments may be a choice for HR+/HER2− metastatic breast cancer patients experiencing severe visceral metastasis.