Breast MR imaging changes after neoadjuvant chemotherapy: correlation with molecular subtypes.

OBJECTIVE MRI is the imaging technique that is best suited to evaluating the response to neoadjuvant chemotherapy for locally advanced breast cancer. We aimed to a) quantify the response in the molecular subtypes, b) describe the morphological and dynamic variation, and c) determine whether the molecular phenotype changes after chemotherapy. MATERIAL AND METHODS This is a retrospective study of 75 carcinomas in 69 patients who underwent MRI both before and after neoadjuvant chemotherapy. The response to treatment was classified as a) complete response, b) major partial response, c) minor partial response, or d) no response. We quantified the response in each molecular subtype (Luminal A, Luminal B, Her2+, and triple negative). The morphological changes were classified as a) concentric reduction, b) fragmentation, c) ductal enhancement, or d) necrosis. The dynamic changes affected the maximum intensity peak and the post-initial enhancement. RESULTS In the 4 molecular subtypes, the 4 types of response were seen. The response was good in 84.6% of the triple negative subtype, in 76.9% of the Luminal B subtype, in 75.6% of the Luminal A subtype, and in 69.2% of the Her2+ subtype. The predominant morphological change was concentric reduction (75%). The predominant dynamic change was a decrease in the maximum intensity peak (<100% in 64.2%), and type I or II curves were seen in 85.7%. CONCLUSIONS The triple negative subtype responded best to neoadjuvant chemotherapy. The most common changes were concentric reduction and a decrease in the maximum intensity peak, with fewer washout curves. We observed a change in the molecular phenotype between the specimen at diagnosis and the final study in 12.2% of cases.