Hypercalcemia and Flower Cells on Peripheral Smear Revealing Human T-lymphotropic Virus Type 1 (HTLV-1)-Associated Adult T-cell Leukemia/Lymphoma.

Adult T-cell leukemia/lymphoma (ATLL) is a rare, aggressive peripheral T-cell malignancy caused by human T-lymphotropic virus type 1 (HTLV-1), most commonly affecting individuals from endemic regions. Diagnosis is challenging and often delayed due to low clinical suspicion and overlapping features with other hematologic and systemic disorders. A characteristic finding on peripheral blood smear is the presence of "flower cells," atypical lymphocytes with deeply lobulated, petal-like, or cloverleaf nuclei and condensed chromatin, which is considered highly suggestive of acute-type disease. This case describes a 59-year-old female diagnosed with ATLL presenting with severe hypercalcemia and characteristic flower cells on peripheral smear, despite lacking recognized epidemiologic risk factors for HTLV-1 infection.