Palbociclib with Fulvestrant or Letrozole in Endocrine-Sensitive Patients with HR-Positive/HER2-Negative Advanced Breast Cancer: A Detailed Safety Analysis of the Randomized PARSIFAL Trial.

Background: Palbociclib has gained a central role in the treatment of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC). Despite its manageable toxicity profile, venous thromboembolism (VTE) or interstitial lung disease (ILD)/pneumonitis may infrequently occur. Therefore, we provide a comprehensive summary of the safety and tolerability of the combination of endocrine therapy and palbociclib among patients included in the randomized phase 2 PARSIFAL study.
Materials and Methods: Patients with endocrine-sensitive HR+/HER2- ABC and no prior therapy in an advanced setting (n = 486) were randomly assigned 1:1 to receive fulvestrant-palbociclib (FP) or letrozole-palbociclib (LP). Laboratory tests and the incidence of adverse events (AEs) were recorded at baseline and day 1 of each cycle. Progression-free survival (PFS) was estimated for patients with and without VTE.
Results: A total of 483 patients were analyzed. Neutropenia, leukopenia, anemia, asthenia, arthralgia, fatigue, and diarrhea were the most frequent AEs in both groups. Febrile neutropenia occurred in 3 (1.2%) patients of the FP group and in 1 (0.4%) patient in the LP group. Six (2.5%; 0.4% grade 3) patients in the FP group and 6 patients (2.5%; 0.4% grade 3) in the LP group experienced ILD/pneumonitis. Pulmonary embolism was reported in 12 (5.0%) patients in the FP group and 6 (2.5%) patients in the LP group. Advanced age at baseline was the only factor significantly associated with an increased risk of pulmonary embolism (P < .01).
Conclusion: The PARSIFAL data confirmed the favorable safety profile of both palbociclib regimens. VTE and ILD/pneumonitis were occasionally reported, and their early detection allowed patients to continue treatment effectively without detriment to efficacy.
Clinicaltrials.gov Identifier: NCT02491983; https://clinicaltrials.gov/ct2/show/NCT02491983).
(© The Author(s) 2022. Published by Oxford University Press.)