The homozygous deletion of the chromosome 9p21.3 locus, which includes cyclin-dependent kinase inhibitor 2A/B (CDKN2A/B) and methylthioadenosine phosphorylase (MTAP) genes, is one of the most common genomic alterations in cancer. MTAP encodes an essential enzyme in the methionine salvage pathway. Historically, deletions at this locus have been characterized primarily by cell cycle dysregulation driven by CDKN2A/B loss. However, recent studies have revealed that the co-deletion of MTAP exposes profound metabolic vulnerabilities. Loss of the MTAP function increases cellular dependency on protein arginine methyltransferase 5 (PRMT5). Consequently, targeted PRMT5 inhibition effectively induces synthetic lethality specifically in MTAP-deleted tumors. Based on this unique mechanism, the development of novel therapeutic agents exploiting this synthetic lethality is actively underway. In this review, we provide a comprehensive overview of the physiological roles of the MTAP-PRMT5 axis and the mechanistic principles underlying this synthetic lethality in MTAP-deficient cells. Furthermore, drawing upon insights from the analysis of real-world patient data, we discuss the clinical and molecular characteristics of MTAP-deleted tumors, review the landscape of ongoing clinical trials, and explore novel therapeutic strategies.
Ikushima et al. (2026) studied this question.