Abstract PS13-49: Effectiveness of platinum-based chemotherapy for hormone receptor-positive HER2-negative metastatic breast cancer

Abstract

Abstract Background: Platinum-based chemotherapy (CT) regimens have activity in triple-negative breast cancer (TNBC), with overall response rates around 50%. The evidence for activity of these regimens for hormone receptor (HR)-positive breast cancer is scarce. We aimed to evaluate the effectiveness of platinum-based CT for HR-positive HER2-negative metastatic breast cancer. Methods: We evaluated, retrospectively, electronic medical records of patients with HR-positive HER2-negative metastatic breast cancer who have received, at least, 1 dose of platinum-based CT in the metastatic setting from Jan/2015 to May/2020 in a single cancer center. Data on clinical and demographic features, treatment, and outcomes were collected. The primary study endpoint was the clinical benefit rate at 3 months. Secondary endpoints were overall response rate, progression-free survival (PFS), overall survival (OS), and prognostic factors. Results: 244 patients were included. All patients were female, with a median age of 51.5 years, 59% were premenopause, 32.8% were metastatic at diagnosis, and 63.5% had ECOG-PS 0-1 by the time of platinum-based CT initiation. Although tests for hereditary breast and ovarian cancer were not available, 41% of patients met criteria for hereditary cancer testing. Most patients had invasive ductal carcinoma (90.2%), estrogen receptor >10% positive (92.2%), and progesterone receptor >10% positive (69.7%). Main sites of metastatic disease were bone (76.2%), lymph nodes (59.4%), lung (52.9%), and liver (62.7%). The majority of patients had received previous palliative systemic therapy before platinum-based CT; 36.5% had not received previous palliative endocrine therapy (ET), and 30.7% had not received previous palliative chemotherapy. The preferred platinum-based CT regimen was cisplatin plus gemcitabine (68.8%), and a small proportion received single-agent platinum-based CT (14.3%). Forty-three patients (17.7%) started platinum-based CT during hospitalization. Grade 3-4 treatment-related toxicities occurred in 40.9% of the patients. The clinical benefit rate at 3 months was 41.2% in the overall population, 46.7% when platinum-based CT was used as first-line CT, and 38.6% when used as subsequent CT line. Overall response rate was 26.7% in first-line platinum-based CT and 18.1% in subsequent CT line. Median PFS and OS were 3.2 months (95% CI 2.8 - 3.8) and 8.6 months (95% CI 6.8 - 9.9), respectively. One-year OS rate was 37.1% (95% CI 30.5 - 43.7%). Factors associated with worse OS were ECOG-PS 3-4 (HR 1.85, 95% CI 1.21-2.82, P=0.004), presence of liver metastases (HR 1.61, 95% CI 1.16-2.23, P=0.004), and platinum-based CT initiation during hospitalization (HR 1.74, 95% CI 1.18-2.56, P=0.005). Conclusion: Despite some activity of platinum-based CT for HR-positive HER2-negative metastatic breast cancer, especially as first-line CT, response rates were lower than historically observed in TNBC. Platinum-based CT was associated with poor PFS and OS outcomes. Negative prognostic factors for OS were ECOG-PS 3-4, presence of liver metastases, and initiation of the platinum-based CT during hospitalization. Citation Format: Lucas Fernando Uratani, Francesco Sansone Bermejo, Pedro HenriqueShimiti Hashizume, Renata Colombo Bonadio, Laura Testa. Effectiveness of platinum-based chemotherapy for hormone receptor-positive HER2-negative metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS13-49.