Predictors of progression-free survival in patients with metastatic breast cancer receiving palbociclib with letrozole

Abstract

Background Palbociclib with endocrine therapy is a first line treatment for patients with estrogen receptor positive (ER+)/ human epidermal growth factor receptor negative (HER2-) metastatic breast cancer (MBC). There is limited data regarding factors which predict progression-free survival (PFS) in patients receiving this treatment. Methods Patients with ER+/HER2- MBC starting palbociclib with letrozole at a UK cancer centre from May 2017 - Dec 2020 were retrospectively identified. Baseline patient and treatment characteristics were obtained from electronic records. PFS was calculated from date of MBC diagnosis to Mar 2021. Results 61 patients were identified with mean age 63 � 1.3 years. 2 were male. 58 (95%) were treatment naive and 3 (5%) had received a single chemotherapy line. The table shows further data. Median PFS was 27.9 months (95% CI 21.3-34.5). Patients with performance status (PS) 0 (HR 0.32, 95% CI 0.13-0.80, p=0.010), no liver metastases (HR 0.46, 95% CI 0.21-1.00, p=0.046) or bone only (non-visceral) metastases (HR 0.36, 95% CI 0.14-0.95, p=0.034) had a longer PFS than patients without these characteristics. Median PFS was 17.2 months (95% CI 6.9-27.5) in patients with liver metastases compared to 30.7 months (95% CI 23.5-37.9) in patients without. Patients with bone only metastases or PS 0 did not reach median PFS. Age, comorbidities, menopause, histology, grade, number of metastatic sites, de novo vs recurrence, dose reduction or toxicity did not predict PFS (p>0.05). In patients with recurrence, previous chemotherapy, mastectomy, relapse on endocrine treatment or relapse within 5 years were not predictive of PFS (p>0.05). Conclusions Median PFS was similar to that in the PALOMA-2 study. PS ?1, liver metastases or any visceral metastases were associated with a significantly shorter PFS. This suggests PS and metastatic pattern are important predictors of PFS and could be used to influence frequency of monitoring in patients with MBC receiving palbociclib.