Myosteatosis: A Distinct, Early and Targetable Novel Biomarker of Cancer Prognosis

Background: Myosteatosis-fat infiltration within skeletal muscle-is emerging as a critical yet underappreciated determinant of cancer outcomes. Although historically overshadowed by sarcopenia and cachexia, myosteatosis is now recognized as a distinct and early muscle phenotype that carries significant prognostic implications across multiple tumor types. Despite its relevance, foundational gaps remain in our understanding of its mechanisms, clinical significance, and therapeutic potential. The goal of this manuscript is to review the current literature to identify the unique characteristics, prevalence, biological and other etiological mechanisms of myosteatosis and its role as an early biomarker in cancer treatment, recurrence, and prognosis. Methods: A review of the evidence from epidemiological, laboratory and other observational studies with regard to the definition of the biomarker, its biological mechanism, its prevalence in cancer patient populations and the gaps in the research was conducted. Results: Retrospective studies utilizing CT imaging reveal that myosteatosis is highly prevalent in cancer populations and independently associated with mortality, treatment toxicity, postoperative complications, functional decline, and survivorship outcomes. Unlike sarcopenia, which primarily reflects loss of muscle mass, myosteatosis reflects impaired muscle quality, metabolic dysfunction, and lipid derangements. Importantly, it appears early in the trajectory of muscle deterioration-well before irreversible cachexia develops-making it a strategic point for intervention. Conclusions: Despite strong associations with clinical outcomes, the biological underpinnings, clinical applications, and modifiability of myosteatosis remain poorly defined. A coordinated research agenda focused on mechanistic discovery, biomarker standardization, and targeted interventions is essential to improving survival, treatment tolerance, and quality of life for patients across the cancer continuum.