The studies by Relling et al. [178] and Singh et al. [179] highlighted the importance of the analysis of variants in TPMT and NUDT15 in cases of leukemia/lymphoma, given that some polymorphisms in these genes lead to the dysregulation of the metabolism of the therapeutic agents, thioguanine and mercaptopurine, thus suggest that knowing the TPMT polymorphisms and NUDT15 is relevant at the start of therapy because allows for an appropriate chemotherapy dosage, thereby avoiding toxicity [178,179]. The gene discussed is NUDT15; the disease is leukemia.