#00066582

A 52-year-old woman diagnosed in 2023 with acute myeloid leukemia secondary to JAK2-positive essential thrombocythemia received induction therapy with daunorubicin and cytarabine followed by allogeneic hematopoietic stem-cell transplantation, achieving complete morphologic remission with negative minimal residual disease. In November 2025, she presented with progressive dyspnea. Chest radiograph (Panel A) revealed bilateral pleural effusions, and thoracentesis was performed. Cytocentrifuged pleural fluid smears stained with May–Grünwald–Giemsa showed medium- to large-sized blast-like cells with irregular nuclei, prominent nucleoli, basophilic cytoplasm, vacuoles, and cytotoxic granulation (Panel B). Some cells were in mitosis (Panel C). Flow cytometry of pleural fluid showed CD34+, CD117+, CD33+, CD13+, CD123+, CD15±, and CD10− expression (Panel D). Cytologic evaluation confirmed atypical hematopoietic cells compatible with blasts (Panel E). Bone marrow examination remained unremarkable. This case highlights that extramedullary relapse may occur despite negative bone marrow findings and should be considered in patients with unexplained pleural effusion and prior leukemia.

Panel A. Posteroanterior chest x-ray

Panel B. Pleural fluid x40. Stain: May–Grünwald–Giemsa

Description: Cytocentrifuged preparation of pleural fluid showing medium to large-sized cells with irregular nuclei containing one or more prominent nucleoli. The cytoplasm is basophilic with substantial cytoplasmatic vacuolation and, in some cells, conspicuous cytotoxic granulation.

Panel C. Pleural fluid x100. Stain: May–Grünwald–Giemsa

Description: Cytocentrifuged preparation of pleural fluid showing medium to large-sized cells with irregular nuclei containing one or more prominent nucleoli. The cytoplasm is basophilic with substantial cytoplasmatic vacuolation and, in some cells, conspicuous cytotoxic granulation. The cell marked with the arrow shows mitosis of immature myeloid cells.

Panel D. Flow cytometry of pleural fluid

Panel E. Pleural fluid cytology. Trichrome acid