Metastatic Alveolar Rhabdomyosarcoma with Occult Primary Tumor in an Adult: A Case Revealed by Trephine Biopsy

Introduction: Rhabdomyosarcoma (RMS) is a malignant tumor, commonly seen in children and adolescents but rare in adults. In children, RMS present in the head and neck, genitourinary tract, or extremities, while in adults, it mostly occurs in the extremities, rarely in head and neck region.  Case Details: A 60-year-old man, with Type2 diabetes mellitus and Alveolar rhabdomyosarcoma (ARMS) with unknown primary under chemotherapy since1 year, came with the complaints of fever, generalised weakness since 1 month. Complete blood count showed Pancytopenia with Haemoglobin - 6.9 g/dl, Total leucocyte count - 2.4x106 /μL, Platelet count - 53x103 /μL. PET- SCAN revealed increase FDG uptake in axial and appendicular skeletal marrow. Bone marrow study showed suppression of trilineage haematopoiesis with 80% atypical elongated cells with hyperchromatic nuclei and abundant eosinophilic cytoplasm, favouring rhabdomyosarcoma cells with focal areas of necrosis. Patient continued chemotherapy with blood transfusions and on regular follow-up.  Conclusion: ARMS is characterized by aggressiveness and metastatic tendencies. It spreads to lungs, bone marrow, liver and brain. This case highlights a rare case of ARMS with occult primary metastasis in the lymph node and bone marrow, making hematopathological analysis essential for diagnosis and understanding disease progression.