Breast density change as a predictive surrogate for response to adjuvant endocrine therapy in estrogen receptor-positive breast cancer.

e21160 Background: Previous studies showed that anti-estrogen therapy lowers mammographic breast density (MD). We hypothesized that the short-term change of breast density can be a surrogate marker predicting response to adjuvant endocrine therapy (ET) for breast cancer. Methods: We analyzed data of 1,065 estrogen receptor (ER)-positive breast cancer patients who underwent surgery between 2003 and 2006 and received at least 2 years of ET including tamoxifen and aromatase inhibitor. MD was measured using Cumulus software 4.0 and expressed as a percentage. MD reduction was defined as an absolute difference between the MD of two mammography images: taken preoperatively and 8-20months after the start of adjuvant ET.. Results: After median follow up of 68.8 months, overall recurrence rate was 7.5% (80/1065). Mean MD reduction was 5.9% (-17.2 to 36.9). In a logistic regression analysis, age<50, high preoperative MD, and longer interval between start of ET to the 2nd mammogram were significantly associated with higher MD reduction (p value<0.05). In a survival analysis using Cox model, tumor size (>2cm), lymph node positive, high Ki-67 (≥10%), and lower MD reduction were independent factors significantly associated with recurrence-free survival (p<0.05). The hazard of recurrence increased proportionally according to the less degree of MD reduction. Conclusions: MD change during short-term use of adjuvant ET was a significant predictive factor for long-term recurrence in ER-positive breast cancer. It is urgent to develop effective treatment strategy in patients who have less MD reduction in spite of about 1 year of ET.