Contribution of skeletal muscle to cancer immunotherapy: A focus on muscle function, inflammation, and microbiota

•This review discussed the effects of low muscle mass (sarcopenia/cachexia) on immune checkpoint inhibitors of immunotherapy.•Studies are conflicting to some extent, which may be partly due to the definitions and measurement methods of muscle depletion.•Chronic inflammation, immune cells, and gut microbiota may play an important role in regulating the efficacy and immune-related adverse events of immunotherapy under the condition of low muscle mass (sarcopenia/cachexia).•Nutritional interventions may be very important for patients with cancer who are planning to receive immune checkpoint inhibitors in the future and will offer researchers a new insight into immunotherapy. [Display omitted] Sarcopenia, characterized by degenerative and systemic loss of skeletal muscle mass and function, is a multifactorial syndrome commonly observed in individuals with cancer. Additionally, it represents a poor nutritional status and indicates possible presence of cancer cachexia. Recently, with the extensive application of cancer immunotherapy, the effects of sarcopenia/cachexia on cancer immunotherapy, have gained attention. The aim of this review was to summarize the influence of low muscle mass (sarcopenia/cachexia) on the response and immune-related adverse events to immunotherapy from the latest literature. It was revealed that low muscle mass (sarcopenia/cachexia) has detrimental effects on cancer immunotherapy in most cases, although there were results that were not consistent with this finding. This review also discussed potential causes of the paradox, such as different measure methods, research types, muscle indicators, time point, and cancer type. Mechanically, chronic inflammation, immune cells, and microbiota may be critically involved in regulating the efficacy of immunotherapy under the condition of low muscle mass (sarcopenia/cachexia). Thus, nutritional interventions will likely be promising ways for individuals with cancer to increase the efficacy of immunotherapy in the future, for low muscle mass (sarcopenia/cachexia) is an important prognostic factor for cancer immunotherapy.