Role of Pectoralis Muscle Analysis in Breast Magnetic Resonance Imaging for Body Composition Evaluation Before and After Neoadjuvant Chemotherapy for Breast Cancer.

: sarcopenia is a physical condition characterized by the loss of muscle mass and strength; it is associated with worse outcomes in oncological diseases and is recognized as an independent predictor of poor survival. The aim of our work is to evaluate the correlation between the pectoralis muscles area (PMA) calculated in breast MRI examinations and the body composition parameters assessed in CT examinations, in order to identify a threshold useful for diagnosing sarcopenia in breast cancer patients who are candidates for neoadjuvant chemotherapy (NACT), so as to be able to provide the correct nutritional counselling. : we included 116 patients with non-metastatic breast cancer, who were studied with MRI before and after NACT, in the 2018-2023 period. All patients were categorized according to age, weight, height, and BMI. Using MRI scans, both before and after treatment, we measured the PMA at the level of the sternal angle of Louis and evaluated the changes caused by NACT, and we performed the same procedure for CT body composition parameters. : the ROC we calculated describes the ability of the PMA to discriminate sarcopenic patients from non-sarcopenic ones, identifying an optimal cut-off of 20.55, which achieves a specificity of 92%. The variations in PMA after NACT showed a strong, statistically significant association with the variations in all CT body composition parameters. : these results introduce the possibility of also assessing body composition in breast MRI. The novelty in this study is to have estimated, on the basis of these correlations, a cut-off value that reflects the skeletal muscle index threshold for the definition of sarcopenia that is usually used.