Mutations in sterile alpha motif domain and histidine–aspartate domain–containing protein 1 (SAMHD1) are found in a neurodevelopmental disorder, Aicardi–Goutières syndrome, and cancers, and SAMHD1, which is a deoxynucleoside triphosphate (dNTP) triphosphorylase, was identified as a myeloid-specific HIV-1 restriction factor. Here, SAMHD1 is linked to cancer.