1093 Background: The survival outcomes of postmenopausal women with invasive lobular carcinoma (ILC) are similar to invasive ductal carcinoma (IDC) when treated with aromatase inhibitor, but inferior when treated with tamoxifen. We sought to investigate the survival outcomes of premenopausal ILC when compared to IDC using a population-based analysis. Methods: We used Surveillance, Epidemiology, and End Results data (SEER) between 1990 to 2015 to identify premenopausal patients (defined as < 50 years old), diagnosed with stage I to III IDC or ILC. Breast Cancer Specific Survival (BCSS) was assessed using log-rank test and piecewisecox models. Annual hazard of BCCS for hormone receptor positive (ER+) ILC and ER+ IDC were calculated from year 0 to 20 and defined as the proportion of patients with a BCSS event during a 1-year interval. Results: The study includes a total of 170,352 pts diagnosed with either IDC (n = 158,733) and ILC (n = 11,619). 71% of IDC and 95% of ILC pts were ER+. Median age was 44 years old and median follow up was 90 months(IQR 40-151 months). Survival analysis revealed a significant time-dependent effect of histology for BCSS (p < .0001). When compared to IDC, ILC pts had better BCSS in the first 10 years after diagnosis (HR 0.73, 95% CI 0.68-0.78), but worse BCSS outcome after year 10 (HR 1.80, 95% CI 1.59- 2.03). Similar results were observed when adjusting for ER status, histologic grade and stage on multivariate analysis. Among pts ≤ 35 years old(n = 371 ILC; 18086 IDC) survival analysis revealed a non-significant trend towards inferior outcome for ILC compared to IDC throughout the whole follow-up period (HR = 1.2 95% CI 0.96-1.52). Annual hazard of BCCS events showed a peak at year 5 for both IDC and ILC. In the subset of IDC, we noticed a decreasing hazard of BCSS from years 6 through 20. By contrast, in the subset of ILC, we observed higher frequencies of BCSS from years 6-20 when compared to IDC (p < 0.0001). Conclusions: In this population-based analysis, premenopausal ILC had worse BCSS estimates when compared to premenopausal IDC. This is explained by a higher incidence of late events in the subset of ILC when compared to IDC.
72TiP ROSALINE: A phase II, single-arm, neoadjuvant study of targeting ROS1 in combination with endocrine therapy (ET) in invAsive Lobular carcINoma of the brEast
