Furthermore, in this case, the results of NGS for the sensitivity of the tumor to common chemotherapeutic drugs revealed CYP2B6*6 polymorphism, i.e., the simultaneous occurrence of p.Q172H and p.K262R heterozygous mutations in both exons 4 and 5 of the CYP2B6 gene; this, in turn, reduces the in vivo activity of the 2B6 enzyme and decreases its effects on drug metabolism, leading to increased toxic adverse effects of cyclophosphamide and isocyclophosphamide (9). The gene discussed is CYP2B6; the disease is neoplasm.