Low skeletal muscle mass (LSMM) predicts relevant clinical outcomes in oncologic patients. The purpose of this study was to perform a meta-analysis of data regarding associations between LSMM and treatment response (TR) in oncology. MEDLINE, Cochrane, and SCOPUS databases were screened for relationships between LSMM and TR in oncologic patients up to November 2022. Overall, 35 studies met the inclusion criteria. The meta-analysis was performed using RevMan 5.4 software. The collected 35 studies comprised 3858 patients. In 1682 patients (43.6%), LSMM was diagnosed. In the overall sample, LSMM predicted a negatively objective response rate (ORR), OR = 0.70, 95% CI = (0.54-0.91), p = 0.007, and disease control rate (DCR), OR = 0.69, 95% CI = (0.50-0.95), p = 0.02. In the curative setting, LSMM predicted a negatively ORR, OR = 0.24, 95% CI = (0.12-0.50), p = 0.0001, but not DCR, OR = 0.60, 95% CI = (0.31-1.18), p = 0.14. In palliative treatment with conventional chemotherapies, LSMM did not predict ORR: OR = 0.94, 95% CI (0.57-1.55), p = 0.81, and DCR: OR = 1.13, 95% CI (0.38-3.40), p = 0.82. In palliative treatment with tyrosine kinase inhibitors (TKI), LSMM did not predict TR: ORR, OR = 0.74, 95% CI (0.44-1.26), p = 0.27, and DCR, OR = 1.04, 95% CI (0.53-2.05), p = 0.90. In palliative immunotherapy, LSMM tended to predict ORR, OR = 0.74, 95% CI = (0.54-1.01), p = 0.06, and predicted DCR, OR = 0.53, 95% CI = (0.37-0.76), p = 0.0006. LSMM is a risk factor for poor TR in curative chemotherapy in the adjuvant and/or neoadjuvant setting. LSMM is a risk factor for treatment failure in treatment with immunotherapy. Finally, LSMM does not influence TR in palliative treatment with conventional chemotherapy and/or TKIs. • Low skeletal muscle mass (LSMM) predicts treatment response (TR) to chemotherapy in the adjuvant and/or neoadjuvant setting. • LSMM predicts TR in immunotherapy. • LSMM does not influence TR in palliative chemotherapy.