Palbociclib Plus Endocrine Therapy Versus Chemotherapy: Outcomes in Metastatic Breast Cancer
Posted: Friday, January 17, 2020
According to the phase III PEARL study, presented at the 2019 San Antonio Breast Cancer Symposium (Abstract GS2-07), the combination of palbociclib plus endocrine therapy did not appear to improve survival outcomes in patients with metastatic breast cancer when compared with capecitabine therapy. According to Miguel Martín, MD, PhD, of the Spanish Breast Cancer Group, Madrid, and colleagues, “No superiority of [palbociclib plus endocrine therapy] was observed in the luminal subgroup either. Treatment with [palbociclib plus endocrine therapy] was generally better tolerated than capecitabine.”
The study included two successive cohorts of patients with metastatic breast cancer. The first cohort (n = 296) consisted of patients who were randomly assigned 1:1 to palbociclib plus exemestane treatment. The second (n = 305) was added after results from cohort 1 indicated that ESR1 mutations may support resistance to aromatase inhibitor treatment and included patients who received palbociclib plus fulvestrant as well as patients who received capecitabine therapy.
In cohort 2, treatment with palbociclib plus fulvestrant resulted in an inferior median progression-free survival of 7.5 months versus 10.0 months for capecitabine. Similarly, capecitabine resulted in an improved overall response rate of 33.3% versus 26.7% for palbociclib plus fulvestrant. A total of 74.4% of patients underwent breast cancer subtype analysis, and 89.1% of patients receiving palbociclib plus exemestane and 91.5% of patients receiving capecitabine were found to have luminal tumors. Among patients with luminal tumors, capecitabine continued to result in improved median progression-free survival outcomes, at 10 months versus 7.5 months for palbociclib plus fulvestrant.
Among patients from either cohort with an ESR1 mutation, capecitabine still maintained superiority in measured outcomes. At a median follow-up of 19 months, the median progression-free survival with palbociclib plus exemestane was 8.0 months versus 10.6 months with capecitabine. Likewise, the overall response rate was 27.8% with palbociclib plus exemestane versus 36.9% with capecitabine. When 79.6% of this patient subgroup underwent subtype testing, 89.2% of patients receiving palbociclib plus exemestane and 91.8% of patients receiving capecitabine were found to have luminal tumors. Again, median progression-free survival was superior with capecitabine than receiving palbociclib plus exemestane.
The most commonly noted toxicity of grade 3 to grade 4 with combination treatment was neutropenia, occurring in more than half of patients receiving palbociclib plus exemestane or fulvestrant. Hand and foot syndrome disproportionately affected patients undergoing capecitabine treatment.
Disclosure: For full disclosures of the study authors, visit abstractsonline.com.
