LAUSR

580Background: NSABP B-41, randomly assigned 529 patients with HER2 positive breast cancer to receive neoadjuvant trastuzumab, lapatinib, or the combination, with weekly paclitaxel following doxorubicin and cyclophosphamide x 4. No significant difference in pCR was found among three arms (Robidoux 2013), but overall survival was significantly increased for patients who obtained a pCR (Robidoux 2016). This study evaluated outcomes in B-41 based on intrinsic subtype. Methods: H&E slides were reviewed by study pathologist for areas of invasive carcinoma having > 10% tumor cells. RNA was isolated and hybridized to the “RUO-PAM50” CodeSet (NanoString Technologies). Intrinsic PAM50 subtype was determined for each sample. Contingence-table analyses were used to compare pCR breast and nodes (ypT0/is ypN0) among intrinsic subtypes and Kaplan-Meier estimates and Cox models were used to compare event-free survival and overall survival among subtypes. Results: Core biopsy samples from 276 patients, prior to therapy, ...