SEER analysis of 9-year breast cancer specific mortality (BCSM) in patients (pts) with invasive lobular breast cancer (ILC) assessed by the 21-gene Breast Recurrence Score assay.

Abstract

554 Background: Linking of the results of the 21-gene Breast Recurrence Score (RS) commercial assay to SEER registries provides opportunity to assess real world prognostic performance of the assay in important subgroups of early breast cancer (BC). ILC is less common than invasive ductal carcinoma (IDC) and the performance of the RS assay in ILC is of interest. The relationship between RS results and 5-year BCSM in patients with ILC was reported based on a linkage in 2015 at this meeting in 2017. Here we present a comparison of 9-year BCSM of ILC vs IDC from a linkage update in 2019. These results will be updated further based on a new linkage of RS data to be completed in April 2023. Methods: Eligible pts had 0-3 axillary nodes at initial surgery, were hormone receptor positive and HER2-negative with a RS result, had no prior malignancy, and were diagnosed between January 2004 and December 2012. Pts with ICD-O-3 code 8520 were categorized as ILC and those with code 8500 as IDC. 9-year BCSM of both cohorts was estimated using actuarial methods. Multivariable Cox proportional hazards models characterized association between RS results and BCSM. Results: Of 89818 pts, 9835 (11.0%) had ILC and 64669 (72.0%) had IDC. Among pts with ILC, median age was 60 years; 12.5% were N1 and 28.4%, 63.7% and 7.9% were grade 1, 2 and 3. Median follow-up was 84 months. Chemotherapy (CT) use and BCSM increased with increasing RS result in both cohorts. After adjusting for age, race, tumor grade, tumor size, nodal status, and histologic subtype, the RS result was independently associated with BCSM ( p < .001) in both ILC and IDC. Conclusions: In this linked SEER analysis of pts with ILC or IDC, the RS results were prognostic for 9-year BCSM, regardless of nodal status. [Table: see text]