Introduction: Adriamycin and cyclophosphamide (AC) combination chemotherapy is one of the common regimens used for breast cancer and in metastatic breast cancer with oligo-metastasis. (1) AC combination chemotherapy regimen is associated with adverse drug reactions like myelosuppression, gastrointestinal toxicity, cardiotoxicity, peripheral neuropathy, and hand-foot syndrome. (2),(3),(4) It has been noticed from previous studies that the metabolism-related gene GSTP rs 1695 homozygous mutant allele has been associated with higher incidences of myelotoxicity and gastrointestinal toxicity post-combination chemotherapy regimens. (5) Case report: A 55-year-old female patient presented with the incidence of grade 3 febrile neutropenia and myelosuppression, 8 days following AC infusion. The patient also has symptoms of grade 2 peripheral neuropathy and diarrhea. She was treated as an inpatient from the local hospital with pegfilgrastim, packed RBC transfusion, and intravenous antibiotics for febrile neutropenia. She recovered completely with this treatment and was discharged without any sequelae or complications. She was then tested for the GSTP rs 1695 gene which revealed the homozygous mutant variant (GG allele). When reporting the causal association of the adverse drug reaction, it comes under the “possible” category of WHO causality assessment. Conclusion: Myelosuppression, Diarrhea, and other adverse events following AC combination chemotherapy can be related to the Genetic polymorphism in GSTP rs 1695 double mutant homozygous allele (GG ) and its altered drug metabolism effects. The Adverse drug reaction comes under the “Possible” Category of WHO causality assessment. Key Words: Adriamycin, Myelosuppression, Cyclophosphamide, Hand-foot syndrome, GSTP rs1695