Risk stratification based on a prognostic factor index among patients with HR+, HER2- MBC.

e12516 Background: Patient and tumor characteristics, such as tumor grade (TG), site of metastases, hormone receptor status, and endocrine resistance, affect the prognosis for patients (pts) with HR+, HER2- metastatic breast cancer (MBC). This study explored the impact of multiple clinical prognostic factors on pt overall survival (OS) and real-world progression-free survival (rwPFS). Methods: This retrospective study used electronic health record (EHR) data of US pts from a network of community oncology practices maintained in the Vector Oncology Data Warehouse from 1/1/2008 to 4/30/2017. Eligibility included HR+, HER2- MBC diagnosis in 2008 or later and prior systemic therapy for MBC. An index variable was created to assess the effect of multiple clinical prognostic factors collectively, including liver metastases (LM), primary endocrine resistance (PER) (Cardoso F et al. 2018), negative progesterone receptor (PR-) status, and high TG. Pts were grouped based on the number of prognostic factors present at MBC diagnosis: 0, 1, and 2+. Differences in rwPFS and OS from start of first line therapy were evaluated by Kaplan-Meier method and multivariable Cox proportional hazards regression. Results: Eligible pts (n=378) had a mean age of 60.3 years. Among these 57.1% were white, 36.5% were de novo metastatic, 22% had LM, 27.2% had high TG, and 27.1% were PR- at baseline. Among all pts, 170 (45%) had received endocrine therapy as first-line treatment, followed by chemotherapy (28%), CDK4 & 6 inhibitor (17%), or other anti-cancer treatment (9%). After adjustment, rwPFS and OS were significantly (p<.05) shorter in pts with 1 and 2+ clinical prognostic factors compared to pts with none (Table). Conclusions: Among pts with HR+, HER2- MBC, these data demonstrate the heterogeneity in pt survival outcomes depending on the presence and number of prognostic factors. Further research should explore the collective importance of these prognostic factors in treatment decisions. [Table: see text]