133P Clinico-pathological predictors of outcome in the (neo)adjuvant setting of luminal/HER2-negative invasive lobular breast cancer (ILC)

The currently adopted prognostic factors for ILC are usually borrowed from the ductal histotype, despite the differences in terms of clinico-pathological features and outcome. Thus, the aim of this analysis was to more precisely stratify the prognosis of ILC undergone (neo)adjuvant therapy, and to explore the addition of chemotherapy (CT) to endocrine therapy (ET) in adjuvant setting. Clinico-pathological data of consecutive patients (pts) affected by pure luminal/HER2-negative ILC (stage I-III), undergone surgery, were collected into 2 cohorts according to treatment setting: 1) adjuvant; 2) neoadjuvant. Independent predictors of overall- and disease free- survival (OS/DFS) were investigated with a Cox model, taking into account: 1) a previously validated prognostic score combining clinico-pathological factors (independently predicting the risk of recurrence and death) and clustering pts into 3 classes (low/intermediate/high risk: <2/=2/>2 score) in adjuvant cohort; 2) the pCR and CPS-EG score in neoadjuvant cohort. Data from 471 pts were gathered. Adjuvant/neoadjuvant cohorts: 386/85 pts (median follow up 86 months [Interquartile range (IQR) 62-124]/96 months [IQR 53-130]). In the adjuvant cohort, 10-yrs DFS was 85%, 72% and 55% in pts with low, intermediate and high-risk score (p<0.001); 10-yrs OS was 99%, 89% and 96% (p=0.06), respectively. Overall, DFS and OS were not significantly improved with CT (administered in 107 pts, 28%) in the overall sample, neither according to stage and prognostic score. In the neoadjuvant cohort, with a pCR rate of 7.1%, no statistically significant difference was found in DFS according to pCR: 5-yrs/10-yrs DFS was 76.6%/80.0% and 42.0%/80% in pts without and with pCR (p=0.34). Conversely, the CPS-EG score was able to distinguish into 2 prognostic groups (CPS-EG≤2 and >2): the 10-yrs DFS was 51% vs. 38% (p=0.028) and 10-yrs OS 86% vs. 66.2% (p=0.009), respectively. While the combination of clinico-pathological factors is able to discriminate the prognosis of ILC, no predictive role for the benefit of adjuvant CT was found. In the neoadjuvant setting, the CPS-EG score stratifies ILC pts according to outcome, more powerfully than pCR.