Chemosensitivity based on pathologic complete response in very young patients with ER-positive breast cancer: a large, multicenter, observational study

Abstract Background In estrogen receptor (ER)-positive breast cancer, young age is associated with poor prognosis. Several reports have suggested hormonal mechanism as the possible reason. Conversely, very young patients respond better to chemotherapy, and chemotherapy is less effective in ER-positive tumors than in ER-negative tumors. The authors tried to evaluate the chemoinsensitivity of very young patients with ER-positive breast cancer by pathologic complete response (pCR) after neoadjuvant chemotherapy excluding the effect of endocrine treatment to the extent possible. Methods We collected individual patient data from 1992 to 2013 from the Korean Breast Cancer Society (KBCS). Total 1,048 ER-positive and 797 ER-negative patients aged <50 years who had been treated with neoadjuvant chemotherapy were included for analysis. We compared the pathologic complete response (pCR) rate between patients aged <35 years with ER-positive tumors and the other groups. Results The proportion of very young patient aged <35years was 14% in ER-positive group and 16.8% in ER-negative group. Although most chracteristics of tumors according to age were comparable in both groups, tumors with high Ki-67 expression were more common in patients under 35years of age than in those aged 35-49years in both groups (P = 0.001). Breast conservation rates were not significantly different according to age in two groups (44.2% vs. 46.8% in ER-positive group, 55.2% vs. 48.0% in ER-negative group). pCR rates of both breasts and axilla were not significantly different according to age in ER-positive group (P=0.71) but significantly better in patients aged <35years in ER-negative group (P=0.009). After adjusting for confounding variables, young patients maintained the higher probability of pCR than older patients in ER-negative tumors. However, the pCR rate did not differ according to age in ER-positive tumors. Conclusions Chemotherapy response based on pCR rates was not better in young patients (<35 years) with ER-positive breast cancer than in older premenopausal patients with ER-positive advanced breast cancer. Young age cannot be a predictive factor of chemosensitivity in ER-positive breast cancer. Different biological characteristics such as high Ki-67 proliferative index should be considered. Trial registration: retrospectively registered