PURPOSE: To evaluate treatment patterns and clinical outcomes of patients who received palbociclib in combination with letrozole in any line of therapy for treatment of hormone receptor–positive, human epidermal growth factor receptor 2–negative metastatic breast cancer in an expanded access program (EAP) in the United States. PATIENTS AND METHODS: A retrospective chart review study was conducted of patients previously enrolled in the palbociclib EAP. Complete data from time of initial diagnosis of metastatic breast cancer until date of chart abstraction were obtained. Clinical outcomes as assessed by site investigators included clinical benefit rate, progression-free survival, and overall survival. Survival was descriptively assessed using Kaplan-Meier methods. RESULTS: Of 238 patients enrolled in the EAP, data from 126 patients were included. Median age was 62.5 years at EAP enrollment; 25% had de novo metastatic disease. Visceral disease was present in 71% of patients. The disease of most patients was heavily pretreated; nearly 60% of patients had received 3 or more prior lines for metastatic disease before initiating palbociclib + letrozole therapy. Most patients (87%) had received prior endocrine therapy, and 68% had received prior chemotherapy for metastatic disease. Patients with prior endocrine therapy for metastatic disease had a clinical benefit rate of 30%, while those with prior chemotherapy had a 26% clinical benefit rate. Patients receiving 2 or more prior lines had 6- and 12-month progression-free survival rates of 35% and 21%, respectively, and 12- and 24-month overall survival rates of 62% and 35%, respectively. CONCLUSION: Most patients derived benefit from palbociclib + letrozole treatment despite having received multiple prior treatment lines for metastatic disease.
