Primary Indolent Acute Promyelocytic Leukemia.

Acute promyelocytic leukemia (APL) is a rapidly progressive subtype of acute myeloid leukemia defined by fusion and characterized by life-threatening coagulopathy. Because the disease typically follows an aggressive course, immediate treatment is essential once APL is suspected. This case report describes an atypical de novo presentation marked by indolent progression rather than the expected aggressive trajectory. A 37-year-old female exhibited gradually declining white blood cell and neutrophil counts over the course of a year, followed by unexplained pancytopenia with severe neutropenia (0.1 × 10/L). Evaluation for nutritional deficiencies and autoimmune disease was unrevealing aside from a positive ANA without clinical features of autoimmunity. Bone-marrow biopsy demonstrated morphologic and flow cytometric findings suggestive of APL, low-level t(15;17), fusion, and concomitant loss and mutation. Despite the indolent clinical presentation and low disease burden, the molecular and cytogenetic findings confirmed the diagnosis of classical APL with loss and mutation. Induction therapy with all-trans-retinoic acid and arsenic trioxide resulted in hematologic remission. This case highlights an unusually indolent form of de novo APL not previously documented in the literature, expanding the recognized clinical spectrum of the disease. The findings emphasize the importance of still considering severe diagnoses, such as APL, when presentations deviate from classical patterns. Atypical clinical trajectories should prompt careful assessment of marrow morphology and immunophenotypic features. Continued characterization of such cases may refine diagnostic criteria and direct individualized approaches to therapy.