Muscle mass loss after neoadjuvant chemotherapy in breast cancer: estimation on breast magnetic resonance imaging using pectoralis muscle area

The loss of skeletal muscle mass is widely considered a predictor of poor survival and toxicity in breast cancer patients. The aim of this study is to evaluate if there is pectoralis muscle area (PMA) variation, reflecting loss of skeletal muscle mass, on consecutive MRI examinations after neoadjuvant chemotherapy.

Time between the MRI examinations, before starting NAC and after completing NAC, was 166.8 ± 50 days. PMA calculated pre-NAC (8.14 cm²) was larger than PMA calculated post-NAC (7.03 cm²) (p < 0.001). According to the Response Evaluation Criteria in Solid Tumors (RECIST) criteria, there were no significant differences between responders (complete or partial response) and non-responders (p = 0.362). The multivariate regression analysis did not show any significant relationships between ΔPMA and age, time between MRI exams, estrogen and progesterone receptor status, human epidermal growth factor receptor status (HER-2), Ki-67 expression, lymph node status, RECIST criteria, histological type, average lesion size, molecular categories, and grade. Inter-reader (k = 0.72) and intra-reader agreement (0.69 and 0.71) in PMA assessment were good.

Pectoralis muscle mass varies in breast cancer patients undergoing NAC and this difference can be estimated directly on standard breast MRI.