Histopathological assessment of anastrozole and tamoxifen as preoperative (neoadjuvant) treatment in postmenopausal Japanese women with hormone receptor-positive breast cancer in the PROACT trial

Purpose The PReOperative 'Arimidex'(R) Compared with Tamoxifen (PROACT) trial compared neoadjuvant anastrozole and tamoxifen in postmenopausal women with large, operable or potentially operable, locally advanced hormone receptor-positive breast cancer. Here, we compare objective clinical responses with histopathological tumor responses to therapy in a cohort of 97 Japanese patients, in order to investigate the consistency of assessment methods and the change in estrogen-receptor (ER) and progesterone-receptor (PgR) status. Methods Histopathological response and the change in ER and PgR status were assessed by comparing pathological specimens collected at baseline (via needle biopsy) with those collected at 3 months (from excised tumors). The response was evaluated using Pathological Response Criteria for Breast Cancer as defined by the Japanese Breast Cancer Society. The patients were randomized to receive anastrozole (n = 48) or tamoxifen (n = 49). Results A numerically greater histopathological response rate was observed when neoadjuvant anastrozole compared with neoadjuvant tamoxifen (35.4 and 12.2%, respectively). The histopathological and clinical objective response rates agreed in 63/97 patients. The ER status of 5/40 patients changed from positive at baseline to negative at 3 months in the anastrozole group compared with 20/37 patients in the tamoxifen group. The PgR status of 16/17 patients in the anastrozole group and of 1/11 patients in the tamoxifen group changed from positive to negative. Conclusions These data support the findings of the main PROACT trial, which confirmed that anastrozole, as compared with tamoxifen, is an effective neoadjuvant endocrine treatment in objective response rates for postmenopausal women with large operable hormone-receptor positive breast cancer. Further follow-up is required to confirm whether histopathological responses to therapy correlate with an overall improvement in survival.