Pathological Complete Response In Basal Subtype Tumors To Predict Improved Distant Metastasis Free Survival In The Nbrst Trial

590Background: In the multi-institutional NBRST study (NCT01479101), conducted from June 2011 to December 2014, 20% of ER+/HER2- patients were classified as Basal subtype by the 80-gene functional subtype signature (80-GS). 3-year event-driven follow-up (FU) is now available. Methods: The 70-gene risk of recurrence signature (70-GS) and 80-GS results were combined to classify patients (Pts) into four molecular subtypes: Basal, HER2, Luminal-B (high risk Luminal), and Luminal-A (low risk Luminal). The rate of pathological complete response (pCR) was previously assessed following neoadjuvant therapy. Here we evaluated FU for these Pts to determine if pCR was predictive of positive outcome using distant metastasis free interval (DMFI) as an endpoint. Results: Of 706 NBRST Pts currently reporting FU, 35% were Basal, 16% HER2, 34% Luminal-B, and 15% Luminal-A. Overall 26% of Pts had a pCR, with notable differences by subtype: 34% in Basal, 67% in HER2, 9% in Luminal-B, and 5% pCR in Luminal-A patients. FU from...