NPM1-mutated AML with starry sky pattern

A 52-year-old women presented with fever, sore throat, white blood cells 181 × 109/L (>80% blasts), Hb 91 g/L, platelets 175 × 109/L. LDH was 1152 U/L. The bone marrow was diffusely infiltrated by blast cells with starry sky pattern due to the presence of numerous tingible body macrophages (upper left, hematoxylin–eosin × 400; T, bone trabecula; the arrow indicates a macrophage). Macrophages were CD68+ (upper right, immune-alkaline phosphatase × 400, arrow) whilst blast cells partially expressed myeloperoxidase (bottom left, immune-alkaline phosphatase × 400, the arrow indicates a negative macrophage) and showed cytoplasmic expression of NPM1 mutant (bottom right, immunoperoxidase, × 400). Mutations of NPM1 (type B) and FLT3-ITD (high ratio: 0,6) were detected. NPM1-mutated acute myeloid leukemia (AML) represents a distinct entity of the World Health Organization classification of myeloid neoplasms that is characterised by unique molecular features,1 typical cytoplasmic dislocation of NPM12 (a protein characteristically located in the nucleolus) and a wide morphological spectrum, including multilineage dysplasia1 and cup-like nuclei. Presentation with a starry sky pattern has not been previously reported. This appearance may at first sight simulate a Burkitt lymphoma/ALL-3 or AML with genotype other than NPM1 mutations and a high proliferative pattern. Demonstration of myeloperoxidase and cytoplasmic expression of NPM1 mutant were diagnostic in our case. The starry sky pattern is consistent with the high tumor burden at presentation, as supported by the increased LDH, the high white blood cell count and the presence of FLT3-ITD. Because of the intermediate risk,1 the patient underwent induction/consolidation therapy, including FLT3 inhibitors, followed by haploidentical hematopoietic stem cell transplantation. She is currently in complete molecular remission, 18 months after allotransplant. Open Access Funding provided by Universita degli Studi di Perugia within the CRUI-CARE Agreement.