Background: At the 2014 ASCO meeting we presented the prognostic STAR score, designed in a dataset of 2,248 pts with low/intermediate grade Lum like BC (HER2-/estrogen receptor [ER]+/G1-2) combining tumor stage (AJCC Cancer Staging 7), progesterone receptor [PR] status, and age at baseline. In this study we included pts with high grade Lum like BC in the neoadjuvant dataset and validated the STAR score in the adjuvant GIM2 trial. Methods: EXPLORATORY COHORT (EC): 3,036 Lum like BC (HER2-/ER+/any grade) pts enrolled in 6 prospective randomized trials and treated with anthracycline-taxane based neoadjuvant therapy. VALIDATION COHORT (VC): 1,610 pts with Lum like BC from the 2x2 factorial randomized GIM2 trial (Del Mastro L, Lancet 2015) investigating dose-dense chemotherapy (CT) and the of addition of 5-FU to epirubicin-cyclophosphamide regimen. All patients received adjuvant endocrine treatment. We used uni/multivariate Cox regression analyses to explore the effect of the score on disease free (DFS) and overall survival (OS). Results: In the EC, multivariate analysis adjusted for CPS+EG score (Mittendorf EA, JCO 2011), CT density, and pCR (ypT0/is ypN0) demonstrated that the STAR score added significant independent information on DFS (p= .007) and OS (p= .002). In the VC, the STAR score added similar prognostic information after adjustment for tumor grade, Ki67 (cut off 20%), and CT density (DFS p< .001; OS p <.001). Multivariate analysis hazard ratios (HR) are shown in the table. Conclusions: The STAR score using stage at diagnosis, PR status and age discriminates Lum like BC with worse prognosis, receiving (neo)adjuvant CT and ET.