Okishiro et al. studied breast cancer patients treated with the combination regimen of 5-fluorouracil, epirubicin, and cyclophosphamide (FEC) and found that genetic polymorphisms in MDM2 SNP309 and TP53 R72P were associated with severe neutropenia and FN, particularly with the C/C genotype in TP53 and the T/T + T/G genotype in MDM2, which correlated with an 83.3% incidence of severe neutropenia and a 62.5% incidence of FN [75]. This evidence concerns the gene MDM2 and neutropenia.