Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 20 1 2026 02 09 117 121 Shalini Singh Department of Pathology and Lab Medicine, All India Institute of Medical Sciences, Rishikesh. Uttarakhand, India Jasmine Porwal Department of Medical Oncology and Hematology, All India Institute of Medical Sciences, Rishikesh. Uttarakhand, India Karthik Kumar Department of Medical Oncology and Hematology, All India Institute of Medical Sciences, Rishikesh. Uttarakhand, India Neha Singh Department of Pathology and Lab Medicine, All India Institute of Medical Sciences, Rishikesh. Uttarakhand, India Uttam Nath Department of Medical Oncology and Hematology, All India Institute of Medical Sciences, Rishikesh. Uttarakhand, India 2024 09 20 2025 12 21 Rhabdomyosarcoma (RMS) is a primitive mesenchymal malignancy of childhood and is very rare in adults. In the presence of a soft tissue mass, bone marrow metastasis of RMS is easy to diagnose. However, RMS can rarely present with extensive marrow replacement, without an obvious primary- a very challenging situation for the pathologist as well as the clinician. Owing to the classical round cell morphology, metastatic RMS is morphologically indistinguishable from acute leukemia, especially when the cells are singly scattered, rather than in clusters. We report a rare presentation of bone marrow metastasis of embryonal RMS in an adult, who presented only with pancytopenia and leucoerythroblastic blood picture. Bone marrow aspiration revealed near total replacement of the hematopoietic elements by atypical blast-like cells, which were singly scattered as well as arranged in loose clusters focally. The case was worked up as acute leukemia. Flow cytometric immunophenotyping ruled out acute leukemia. The trephine biopsy was more in favor of a metastatic tumor; hence, a PET-CT was performed. The scan revealed diffuse uptake in the axial and appendicular skeleton, along with enlarged supraclavicular lymph nodes. An excision biopsy of the lymph node clinched the diagnosis of metastatic RMS, which was confirmed by immunohistochemistry for desmin and Myo-D1. This report highlights a rare case of adult embryonal RMS and emphasizes the importance of a multidisciplinary diagnostic approach for metastatic disease in this population.   https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/2322 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/2322/1124