Real-world outcomes of patients with metastatic endocrine-responsive breast cancer receiving palbociclib-based combinations.

Aim: To describe treatment journey and clinical outcomes after palbociclib initiation in HR+/HER2- breast cancer patients across multiple lines. Materials & methods: Adult patients (n = 559) were identified in a population-based study between January 2018 and June 2020. Results: Median follow-up time was 41.2 months. The starting dose was 125 mg for more than 85% of patients, and a third had dose reduction. Median time on treatment was 30.5 months for palbociclib + aromatase inhibitors for patients that received first-line treatment after metastatic diagnosis, and 12.6 months for palbociclib + fulvestrant across multiple lines, and longer for patients that had a dose reduction during treatment. At 48 months, 59.3 and 27.3% of patients were still alive, respectively. Subsequent lines resulted in median time on treatment of 4.4-7.7 months in both groups. Conclusion: Time on treatment for palbociclib was comparable to data from clinical trials, and follow-up allowed us to examine subsequent treatment after initial treatment failure. Dose reduction was common in the real-world setting and did not adversely affect efficacy.