Effect of Oncotype DX Recurrence Score (RS) on chemotherapy (CT) decision-making by providing information beyond intrinsic subtypes in both luminal A and B breast cancer (BC) patients (pts): A retrospective study in the Spanish population.

e12013Background: St Gallen guidelines recommend the use of Ki67 by IHC as a surrogate marker for luminal A and B BC subtypes, such that pts with luminal B ( ≥ 14%) subtypes should be considered for adjuvant CT. Oncotype DX RS is a predictor of CT benefit. The aim of this study is to assess the distribution of the RS in luminal A and B BC subtypes as defined by Ki67 and to assess treatment changes based on RS. Methods: Data were collected from 210 pts with invasive breast cancer for which Oncotype DX results and pathology data were available. Estrogen (ER) and progesterone (PR) receptor was assessed by immunostaining (cut-off 10% nuclear staining). Ki67 was assessed by IHC [high ( ≥ 14%) and low ( < 14%)]. Grading was performed using the Nottingham grading system. Results: Median age: 50 years (35-78); premenopausal status: 122 pts (58.1%). Median tumor size: 1.7 cm (2-10); Overall, 65.7% of cases had grade II tumors, and 13.3% grade III. All pts had HER2 negative tumors, 90 were luminal A and 120 luminal...