SAMHD1 and breast cancer: Recent studies have demonstrated association of germline SAMHD1 coding variants with having two or more primary cancers in the UK Biobank49 (P = 2.4 × 10−7), and with breast cancer susceptibility50 (P < 1 × 10−4). SAMHD1 has a role in preventing the accumulation of excess deoxynucleotide triphosphates (dNTPs), particularly in non-dividing cells51.