A systematic review and meta-analysis of studies on sarcopenia in breast cancer patients found a significant association between sarcopenia and increased mortality, disease progression, and chemotherapy toxicity. Sarcopenia, defined as reduced skeletal muscle mass and strength, was linked to a 33% higher risk of mortality and a 29% higher risk of disease progression in both non-metastatic and metastatic breast cancer patients. Sarcopenic patients were more likely to experience severe chemotherapy-related toxicities, with an odds ratio of 3.58 for grade 3–4 toxicity. Additionally, sarcopenic patients had a higher rate of pathological complete response (pCR) in neoadjuvant settings. These findings suggest that sarcopenia is an independent predictor of poor outcomes and may influence chemotherapy dosing to better manage individual pharmacokinetic differences. The study highlights the importance of assessing body composition in breast cancer patients, as sarcopenia may be a new factor affecting treatment outcomes and quality of life. The results emphasize the need for further research to understand the mechanisms underlying sarcopenia and its impact on cancer prognosis.A systematic review and meta-analysis of studies on sarcopenia in breast cancer patients found a significant association between sarcopenia and increased mortality, disease progression, and chemotherapy toxicity. Sarcopenia, defined as reduced skeletal muscle mass and strength, was linked to a 33% higher risk of mortality and a 29% higher risk of disease progression in both non-metastatic and metastatic breast cancer patients. Sarcopenic patients were more likely to experience severe chemotherapy-related toxicities, with an odds ratio of 3.58 for grade 3–4 toxicity. Additionally, sarcopenic patients had a higher rate of pathological complete response (pCR) in neoadjuvant settings. These findings suggest that sarcopenia is an independent predictor of poor outcomes and may influence chemotherapy dosing to better manage individual pharmacokinetic differences. The study highlights the importance of assessing body composition in breast cancer patients, as sarcopenia may be a new factor affecting treatment outcomes and quality of life. The results emphasize the need for further research to understand the mechanisms underlying sarcopenia and its impact on cancer prognosis.