DTX-5500 is a genetically targeted enzyme replacement therapy for an immunotherapy target found in tumors with deletion or silencing of the methylthioadenosine phosphorylase (MTAP) tumor suppressor gene. Deletion of MTAP at Chromosome 9p21.3 is the second most common tumor suppressor gene deletion in cancer occurring in ~15% of all solid tumors. Loss of MTAP function provides suppresses antitumor immunity through a noncanonical pathway of immunosuppression. In patients MTAP deletion predicts worse survival, an immunosuppressed tumor microenvironment, and resistance to immune checkpoint inhibitor immunotherapy. There is already an FDA approved genetic diagnostic test for MTAP deletion