Timing to imaging and surgery after neoadjuvant therapy for breast cancer

Neoadjuvant therapy (NAT) is increasingly used in breast cancer (BC), yet, the recommended time interval between NAT completion, preoperative imaging assessment, and breast surgery is not clearly defined. This single-center retrospective study investigated tumor growth between NAT completion and surgery. The analysis included 106 BC patients who received NAT (69% chemotherapy alone, 31% chemotherapy plus anti-HER2 therapy), had post-NAT breast MRI, and definitive surgery between 2012 and 2019. The median time interval between end-of-treatment and surgery was 6 weeks; 90% had surgery within 8 weeks of NAT completion, and 10% had surgery 8-12 weeks after NAT completion. No significant correlation was found between any of the time intervals (i.e., NAT completion-to-surgery, NAT completion-to-MRI, post-NAT MRI to surgery) and the tumor size as captured in the pathology report. The only parameter that was significantly correlated with pathological tumor size was tumor size as measured on the post NAT MRI (P < .0001). The difference in tumor size between post NAT MRI and surgical pathology did not correlate with the time interval between end-of-treatment and surgery. The ratio between residual tumor size on post-NAT MRI and the time interval from the end-of-treatment to surgery, significantly correlated with the tumor size on surgical pathology (P < .0001) suggesting that NAT has a beneficial effect weeks after end-of-treatment. In conclusion, our results suggest that for patients undergoing neoadjuvant chemotherapy, surgery within 4-8 weeks of completing NAT is reasonable, and is unlikely to result in a clinically significant change in residual tumor size.