Skeletal muscle as an endocrine and paracrine organ in breast cancer biology: a narrative review

Upon muscle contraction during exercise and resistance training, skeletal muscle releases an array of bioactive molecules called myokines, allowing it to function as a dynamic endocrine organ. Myokines promote systemic and local effects, influencing metabolism and organ function. These myokines may also promote anticancer activity, particularly in breast cancer, and especially in ER/PR-positive, HER2-negative disease. Myokines may influence breast cancer tumor growth, progression, and treatment outcomes. Exercise oncology offers a unique means of optimizing the endocrine and paracrine actions of skeletal muscle-derived myokines within the clinical management of breast cancer. Therefore, the aim of this review is to integrate mechanistic, preclinical, and clinical evidence linking exercise-induced myokines to breast cancer biology, identify breast cancer-specific regulators of myokine signaling, and outline practical implications for exercise oncology prescription and future clinical trial design.