Potential impact of the 70-gene signature in the choice of adjuvant systemic treatment for ER positive, HER2 negative tumors: a single institution experience.

PURPOSE: We investigated in a single institution series of 124 women with operable breast cancer whether tumor clinicopathological features could predict the 70-gene signature (Mammaprint, MP) results, and whether MP results could help to make decisions for the use of chemotherapy (CT) in patients (pts) with ER positive breast cancer beyond recommendations of international guidelines. RESULTS: Among the 68 ER/PgR positive, HER2 negative tumors, Ki-67 ≥ 20% was the only significant predictor of a high risk-MP among standard clinicopathological features. In candidates for endocrine therapy with undetermined benefit from CT according to international guidelines, MP results would have led to different treatment decisions in 13/46 (28%) and in 20/68 (29%) pts according to NCCN and St. Gallen recommendations, respectively. CONCLUSIONS: Ki-67 independently predicted high risk-MP in ER/PgR positive, HER2 negative tumors. MP results would have led to discordant treatment recommendations in about 30% of cases, generally increasing indication rate for CT. The results of large randomized trials are warranted in order to understand whether we should rely on multigene assays rather than on standard clinicopathological features for treatment decisions.