Background: National guidelines for breast cancer management do not recommend routine imaging during preoperative chemotherapy. Despite this, some clinicians use radiographic results as a surrogate marker of treatment response during the preoperative phase. In this retrospective investigation, we studied the correlation between neoadjuvant clinical decision making, midway imaging results and final pathologic responses. Methods: 394 patients with locoregional breast cancer who received neoadjuvant chemotherapy and definitive surgery within the Henry Ford Health System between 2015-2021 were included. Final pathologic response of patients who completed midway imaging were compared with patients who did not. The primary outcome was overall pathologic response rate. Results: Tumor histology and final pathologic response (PR) was compared in patients who received midway imaging (MI) to those who did not (Table). In the MI group, no statistically significant association between midway radiographic response and final PR was found (p = 0.078). Systemic treatment was changed in 14.7% of patients after MI, there was no association with treatment change and complete PR (p = 0.488), however none of patients who received a treatment change after MI had progressive disease on final PR, compared to 9.7% of patients who did not have a treatment change and had progressive disease on final PR (p = 0.035). Multivariate analyses showed no association between MI and complete PR, irrespective of the histological subtypes. 78.4% of patients had imaging at the end of systemic treatment, prior to surgery. Radiographic response on post-treatment imaging correlated with final PR (p < 0.001). Conclusions: This study did not detect an association between midway imaging during neoadjuvant therapy and a complete pathologic response in locoregional breast cancer, however a correlation was detected between post-treatment imaging response and final pathologic response. Changes to systemic treatment based on midway radiographic findings were not shown to improve the likelihood of complete pathologic response but may reduce risk of progressive disease. Based on this study, midway imaging should not be broadly ordered during preoperative treatment, unless there is concern for progressive disease, in which midway imaging may provide diagnostic benefit.

HR+ = Estrogen and/or progesterone receptor positive; HER2+ = HER2 IHC 3+ score or FISH ratio ≥2; TPC = triple positive cancer; TNC = triple negative cancer