Beyond Mesothelioma: From Diagnostic Biomarker to Therapeutic Opportunity—The Emerging Role of MTAP in Cancer

Methylthioadenosine phosphorylase (MTAP) loss is an emerging biomarker in several human malignancies, mainly due to its frequent co-deletion with CDKN2A on chromosome 9p21. Beyond its diagnostic value, MTAP deficiency has important biological consequences, including metabolic reprogramming, immune microenvironment modulation, and increased dependency on PRMT5-related pathways. This review summarizes the current evidence on MTAP alterations across different tumor types. The role of MTAP immunohistochemistry as a practical surrogate for CDKN2A homozygous deletion is discussed, together with its advantages and interpretative limitations. In addition, the potential predictive relevance of MTAP loss for immunotherapy, antifolate-based treatments, and novel PRMT5-targeted strategies is explored. Overall, MTAP assessment represents a promising tool in modern diagnostic pathology and precision oncology, bridging morphology, molecular alterations, and therapeutic decision-making.