Low skeletal muscle mass (LSMM) is increasingly recognized for its predictive value for adverse events in cancer patients. In specific, the predictive value of LSMM has been demonstrated for anti-cancer drug toxicity in a variety of cancer types and anti-cancer drugs. However, due to the limited sample size and study populations focused on a single cancer type, an overall predictive value of LSMM for anti-cancer drug toxicity remains unknown. Therefore, this review aims to provide a comprehensive overview of the predictive value of LSMM and perform a meta-analysis to analyse the overall effect. A systematic search was conducted of MEDLINE, Scopus, EMBASE, and Cochrane. Inclusion criteria were skeletal muscle mass (SMM) evaluated with computed tomography (CT) or magnetic resonance imaging (MRI), articles published in English, SMM studied in humans, SMM measurement normalized for height, and patients did not receive an intervention to treat or prevent LSMM. A meta-analysis was performed using a random-effects model and expressed in odds ratio (OR) with 95% confidence interval (CI). Heterogeneity was assessed using χ² and I² statistics. The search yielded 907 studies. 31 studies were included in the systematic review. Sample sizes ranged from 21 to 414 patients. The occurrence of LSMM ranged from 12.2% to 89.0%. The most frequently studied cancer types were oesophageal, renal, colorectal, breast, and head and neck cancer. Patients with LSMM had a higher risk of severe toxicity (OR 4.08; 95% CI 2.48–6.70; p < 0.001) and dose-limiting toxicity (OR 2.24; 95% CI 1.28–3.92; p < 0.001) compared to patients without LSMM. To conclude, the predictive value of LSMM for anti-cancer drug toxicity can be observed across cancer types. This information increases the need for further research into interventions that could treat LSMM as well as the possibility to adapt treatment regimens based on the presence of LSMM.

Background: Sarcopenia, defined as the presence of low skeletal muscle mass, is highly prevalent in cancer patients and associated with adverse events and lower survival. Given the chronic inflammation associated with sarcopenia, it is especially relevant in patients receiving immunotherapy. The current research is limited to small sample sizes and single cancer types leaving the overall effect of sarcopenia unclear. This review and meta-analysis examined the prognostic effect of sarcopenia in cancer patients treated with immunotherapy. Methods: A systematic review was conducted using EMBASE, MEDLINE, Cochrane, and Scopus. Studies were included if they investigated the association of baseline low skeletal muscle mass, as measured on CT or MRI and normalised for height, and survival in patients with solid tumours treated with immunotherapy. A meta-analysis of hazard ratios (HR) was performed using a random effects model for overall survival (OS) and progression-free survival (PFS). Results: In total, 48 studies were included in this review, of which 42 were included in the meta-analysis. The prevalence of sarcopenia ranged between 19.5% and 83.6%. The meta-analysis showed an overall prognostic effect of sarcopenia for OS and PFS (HR = 1.58; 95% CI 1.35–1.85; p < 0.0001 and HR = 1.50; 95% CI 1.30–1.72; p < 0.001, respectively). High heterogeneity was present between the included studies, which could possibly be explained by the differences in sarcopenia definition, cutoff values, and measurement techniques. Conclusions: Sarcopenia is a significant adverse prognostic factor for both OS and PFS in patients with solid tumours treated with immunotherapy across cancer types. Further research into the underlying mechanism of sarcopenia and its relation to the immune response and survival is needed. Prospective intervention studies are required to establish the care needed, such as nutrition and exercise, to improve the prognosis of sarcopenic patients.