21-gene recurrence score assay as a predictor of pathological response in neoadjuvant chemotherapy administration for ER-positive/HER2-negative early-stage breast cancer.

e12630 Background: Neoadjuvant chemotherapy (NAC) is an optimal option in early breast cancer, but in ER-positive/HER2-negative (luminal) is still controversial, although a survival benefit has recently been observed when a histological response by symmands method type 0 or I is achieved. The 21-Gene recurrence score assay (Oncotype DX) is a validated test to assess the survival benefit of adjuvant chemotherapy in these patients but its role in neoadjuvant setting is not yet well established unknown. We analyze the correlation between Oncotype DX Recurrence Score result and the pathological response assessed by symmands method. Methods: We analyzed a prospective cohort of 63 early luminal breast cancer patients who received NAC after performing an Oncotype DX test. Patients with an Oncotype DX Recurrence Score result lower 11 were excluded. The median age was 54 years (31-84), initial tumor size was 37 mm (12 -97), 41 patients (65%) had initial nodal involvement and the median Ki67 index was 34% (8 – 85). Results: An Oncotype DX results inferior or equal to 25 (considered as a limited benefit of chemotherapy treatment) was observed in 25 patients (40%) and a Recurrence Score higher than 25 in 38 (60%). Pathological response type 0 was achieved in 5 patients (8%) and type I in 16 (25%). A strong correlation between pathological response type 0 and I and Recurrence Score result in the univariate and multivariate analysis (OR 0,946 p:0,023) was found. We have performed a threshold analysis finding the Oncotype DX the most significant predictor of pathological response (AUC:0,75 p:0,0 01 ) compared to Ki67 (AUC:0,61 p:171), Estrogen receptor (AUC:0,41 p:0,21) and initial tumor size (AUC:0,671 p:0,028). All the patients who achieved a complete pathological response had a Recurrence Score result ≥ 26. Conclusions: The Oncotype DX Recurrence Score could be a useful tool to select early breast cancer patients who will benefit from neoadjuvant chemotherapy. Oncotype DX is the most significant predictor variable of pathological response and patients with a Recurrence Score of 25 or greater are five times more likely to obtain a histological response type 0-1 (OR: 5,3 p < 0,016). In our series the Oncotype DX test reaches the highest rate of complete pathological responses in this group of patients.