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

Objectives: 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. Methods: The retrospective study protocol was approved by our institutional review board. A total of n = 110 consecutive patients (mean age 56 ± 11 years) who were treated with neoadjuvant chemotherapy (NAC) for histologically proven primary breast cancer between January 2017 and January 2019 and in whom tumor response was checked with standard breast MRI were included. Two radiologists calculated the pectoralis muscle cross-sectional area before and after NAC. Results: 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. Conclusions: Pectoralis muscle mass varies in breast cancer patients undergoing NAC and this difference can be estimated directly on standard breast MRI. Key Points: • Pectoralis muscle area variation reflects loss of skeletal muscle mass. • Pectoralis muscle area on MRI is reduced after NAC. • Pectoralis muscle mass loss seems independent from other variables.