This systematic review and meta-analysis evaluates the prevalence and clinical outcomes of sarcopenia in breast cancer patients, focusing on both non-metastatic and metastatic settings. The study aimed to identify any correlation between sarcopenia and patient outcomes, particularly in terms of toxicity and survival. Out of 359 screened studies, 16 were included in the meta-analysis, involving 6130 patients, of whom 5284 had non-metastatic breast cancer. Sarcopenia was defined using computed tomography (CT) scans and expressed as the skeletal muscle index (SMI) or appendicular lean mass index (LMI). The results showed that sarcopenic patients had a 33% higher risk of mortality and a 29% higher risk of disease progression/relapse compared to non-sarcopenic patients. Additionally, sarcopenic patients were more likely to experience grade 3-4 toxicities, with an odds ratio (OR) of 3.58 (95% CI 2.11-6.06, p < 0.0001). In the neoadjuvant setting, sarcopenic patients had a higher rate of pathological complete response (pCR) (OR 2.74, 95% CI 0.92-8.22). The study concludes that sarcopenia is a significant prognostic factor for negative outcomes, especially in terms of toxicity, and suggests that it should be considered in dose selection for chemotherapy to better balance individual pharmacokinetic differences. Further research is needed to explore the deeper mechanisms underlying the relationship between sarcopenia, systemic inflammation, and cancer patient outcomes.This systematic review and meta-analysis evaluates the prevalence and clinical outcomes of sarcopenia in breast cancer patients, focusing on both non-metastatic and metastatic settings. The study aimed to identify any correlation between sarcopenia and patient outcomes, particularly in terms of toxicity and survival. Out of 359 screened studies, 16 were included in the meta-analysis, involving 6130 patients, of whom 5284 had non-metastatic breast cancer. Sarcopenia was defined using computed tomography (CT) scans and expressed as the skeletal muscle index (SMI) or appendicular lean mass index (LMI). The results showed that sarcopenic patients had a 33% higher risk of mortality and a 29% higher risk of disease progression/relapse compared to non-sarcopenic patients. Additionally, sarcopenic patients were more likely to experience grade 3-4 toxicities, with an odds ratio (OR) of 3.58 (95% CI 2.11-6.06, p < 0.0001). In the neoadjuvant setting, sarcopenic patients had a higher rate of pathological complete response (pCR) (OR 2.74, 95% CI 0.92-8.22). The study concludes that sarcopenia is a significant prognostic factor for negative outcomes, especially in terms of toxicity, and suggests that it should be considered in dose selection for chemotherapy to better balance individual pharmacokinetic differences. Further research is needed to explore the deeper mechanisms underlying the relationship between sarcopenia, systemic inflammation, and cancer patient outcomes.