Context-dependent regulation of IL-6 in exercise and colorectal cancer cachexia

Colorectal cancer (CRC) is a common malignancy of the digestive system and remains a major cause of cancer-related morbidity and mortality worldwide. Its development and progression are influenced by genetic susceptibility, lifestyle factors, metabolic dysregulation, and chronic inflammatory states. Cancer cachexia is a multifactorial wasting syndrome characterized by weight loss, skeletal muscle atrophy, metabolic disturbances, and functional decline, which substantially impairs quality of life and survival outcomes in patients with CRC. In this context, interleukin-6 (IL-6) has emerged as a context-dependent regulatory mediator linking inflammation, metabolism, tumor biology, and skeletal muscle wasting. The biological effects of IL-6 are shaped by signaling mode, cellular source, concentration, temporal dynamics, and the broader tumor-host environment. This review discusses the regulatory roles of IL-6 in CRC and CRC-related cachexia, with particular attention to exercise-associated IL-6 responses. Rather than viewing exercise-induced IL-6 as inherently beneficial or antitumor, we emphasize that IL-6 is one component of a broader exercise-responsive network involving metabolic adaptation, immune regulation, skeletal muscle function, and systemic inflammatory remodeling. We also summarize current evidence regarding how exercise modality and intensity may influence IL-6 dynamics, while distinguishing mechanistic and preclinical findings from limited and heterogeneous human data. Overall, IL-6 dynamics may provide a hypothesis-generating framework for understanding exercise responses in CRC-related cachexia, but current evidence is insufficient to support IL-6-guided individualized exercise prescription or therapeutic decision-making in clinical practice.