A rare case report of synchronous occurrence of breast carcinoma and chronic myeloid leukemia: diagnostic and clinical implications

Background: Breast carcinoma is the most common malignancy in females, and while a few cases of second primary solid organ malignancies have been reported, the synchronous occurrence of breast cancer and chronic myeloid leukemia (CML) remains exceedingly rare, particularly in patients without prior cytotoxic treatment. CML, a rare myeloproliferative neoplasm, typically develops following exposure to ionizing radiation or chemotherapy. We present the first reported case from Pakistan of synchronous CML diagnosed during staging workup of breast carcinoma. Case Presentation: A 67-year-old female presented with a 10-month history of left breast itching and a palpable mass. The biopsy revealed invasive breast cancer with focal lobular growth pattern (grade 2), ER/ PR negative and HER2 3+. Laboratory tests showed leukocytosis and thrombocytosis; peripheral smear indicated increased myeloid precursors. Bone marrow biopsy confirmed myeloid hyperplasia without metastasis, and molecular testing detected BCR-ABL fusion, confirming chronic myeloid leukemia. The patient was started on chemotherapy for breast cancer alongside imatinib for CML. Conclusion: Synchronous breast cancer and CML, though rare, should be considered in differential diagnoses when leukocytosis is observed in cancer patients. Early detection and accurate diagnosis are critical for optimizing treatment and improving survival outcomes.