In this study, we also observed, as a protective factor, the association between alleles combination GGGGCC in Luminal A with a partial response, HER2 with gastric (nausea, diarrhea, vomiting, stomatitis, and mucositis), hematological (neutropenia, anemia, and thrombocytopenia) toxicities during chemotherapy treatment, as well as the reduced risk of GGGGTC alleles combination in BC triple negative in stage I–II. This evidence concerns the gene ERBB2 and mucositis.