Evaluating the 21-gene assay Recurrence Score® as a predictor of clinical response to 24 weeks of neoadjuvant exemestane in estrogen receptor-positive breast cancer

Abstract

The aim of this study was to investigate the association between the results of the Recurrence Score (RS) assay and the clinical response to neoadjuvant endocrine therapy in postmenopausal women with breast cancer. Core biopsy samples at baseline and post-treatment surgical samples were obtained from 80 and 77 of 116 patients, respectively, enrolled in the multicenter prospective study of neoadjuvant exemestane therapy (JFMC34-0601). The 21-gene assay was performed after appropriate manual microdissection. The estrogen receptor (ER), progesterone receptor, HER2 and Ki-67 were assayed by immunohistochemistry at a central laboratory. Clinical response was assessed based on the RECIST (Response Evaluation Criteria In Solid Tumors) guideline. Sixty-four core biopsy samples and 52 resection samples met the RS quality requirements. The clinical response rate in those patients with a low RS result (low RS group; 19/32, 59.4 %) was significantly higher than that in those patients with a high RS result (high RS group; 3/15, 20.0 %) (P = 0.015) and similar to that in patients with an intermediate RS result (intermediate RS group; 10/17, 58.8 %). The rates of breast-conserving surgery (BCS) were 90.6 % (29/32) in the low RS group, 76.5 % (13/17) in the intermediate RS group and 46.7 % (7/15) in the high RS group. The odds ratio for BCS adjusted for continuous baseline Ki-67 was 0.114 [95 % confidence interval (CI) 0.014-0.721; P = 0.028] between the high and low RS groups. RS values in pre-treatment samples were highly correlated with those in post-treatment samples (Spearman correlation coefficient 0.745, 95 % CI 0.592-0.846). Our results demonstrate the predictive value of the RS for clinical response to neoadjuvant exemestane therapy in postmenopausal women with ER-positive breast cancer.