Bone marrow metastasis with profound pancytopenia is an extremely uncommon presentation of breast cancer. Advanced breast cancer can frequently metastasize to bone marrow, but bone marrow failure is not typically seen. Very limited data exist regarding the appropriate management of patients with metastatic breast cancer with profound pancytopenia. Our patient's initial presentation of anemia and thrombocytopenia was a diagnostic dilemma, later confirmed as metastatic breast cancer on bone marrow biopsy. After diagnosis, treatment was another challenge as there are no predefined treatment guidelines for these patients. After the initial hormonal therapy failed, our patient showed a good clinical response to chemotherapy and her platelet count improved to baseline. This dramatic response to chemotherapy is rare. Therefore, this case represents a rare instance of a diagnostic and therapeutic dilemma with unusual clinical response to chemotherapy.