Acute Adult T-Cell Leukemia/Lymphoma Mimicking T-Cell Lymphoblastic Lymphoma in the Brazilian Amazon: A Case Report and Narrative Review of Latin American Cases.

Human T-lymphotropic virus type 1 (HTLV-1) infection is asymptomatic in most carriers; however, approximately 5% of infected individuals may develop adult T-cell leukemia/lymphoma (ATLL), a rare and highly aggressive malignancy with poor prognosis. We report a case of acute-type ATLL in an elderly patient from the Brazilian Amazon that was initially suspected to be T-cell lymphoblastic lymphoma, resulting in diagnostic delay. Peripheral blood and bone marrow examinations revealed marked lymphocytosis with characteristic "flower cells," prompting serological testing for HTLV-1. Infection was confirmed by chemiluminescent immunoassay and western blot. The diagnosis was established at the state reference hematology center, highlighting the critical role of cytomorphologic evaluation in endemic regions where HTLV-1 remains underdiagnosed. We additionally present a narrative review of reported ATLL cases in Latin America, emphasizing the frequency of acute presentations, high mortality rates, and diagnostic challenges posed by overlapping immunophenotypic features with other aggressive T-cell neoplasms. This case underscores the importance of maintaining a high index of suspicion for HTLV-1-associated ATLL in tropical settings and reinforces the need for improved diagnostic surveillance in the Brazilian Amazon.