From Solid Tumor to Hematologic Malignancy: A Case Report of Acute Promyelocytic Leukemia Following Breast Cancer Treatment.

Acute promyelocytic leukemia (APL) is a rare and aggressive subtype of acute myeloid leukemia (AML) that typically presents with bleeding tendencies and cytopenias. It is commonly associated with the PML::RARA fusion and, if not recognized early, can lead to severe coagulopathy and early mortality. Although post-cytotoxic therapy APL has been described following exposure to chemotherapy or radiation, its occurrence after breast cancer treatment, especially in patients managed primarily with hormonal therapy, is exceptionally rare. We are reporting a case of a 50-year-old female with estrogen receptor (ER)/progesterone receptor (PR)-positive, human epidermal growth factor receptor 2 (HER2)-negative, grade III invasive ductal carcinoma of the right breast (cT2N1M0), treated with neoadjuvant hormonal therapy (luteinizing hormone-releasing hormone (LHRH) analogs and letrozole) and zoledronic acid, followed by breast-conserving surgery, axillary dissection, and adjuvant radiotherapy. Post-treatment imaging showed no recurrence. One year later, she presented to the emergency department with epigastric and retrosternal pain, melena, dyspnea, and spontaneous bruising. ECG revealed T-wave inversions with elevated troponin I, raising the suspicion of myocardial infarction. Laboratory workup showed leukocytosis, anemia, thrombocytopenia, and 84% abnormal promyelocytes on peripheral smear. Fluorescence in situ hybridization (FISH) was positive for the PML::RARA fusion gene, confirming APL, supported by bone marrow biopsy and flow cytometry. She was initiated on all-trans retinoic acid (ATRA), idarubicin, allopurinol, and steroids due to a high leukocyte count. This case highlights post-cytotoxic therapy APL and its rare presentation following breast cancer treatment.