Methylthioadenosine-DADMe immucillin-A (MTDIA) is a transition-state analog that potently inhibits the human protein 5′-methylthioadenosine phosphorylase (MTAP) at picomolar concentrations and elicits anti-tumor activity against lung, prostate, colon, cervical, head and neck, and triple-negative breast cancers in cell and animal models. Here, MTAP is linked to neoplasm.