POT1 and plasma cell myeloma: Three myeloma risk loci in Table 1 harbor candidate genes proposed to regulate genomic stability in tight association with cell cycle progression: MTAP, CEP120, and POT1. MTAP (methylthioadenosine phosphorylase) at 9p21.3 plays a major role in polyamine metabolism and is important for the salvage of adenine and methionine.