Intra-abdominal desmoplastic small round cell tumor with extensive extra-abdominal involvement.

Intra-abdominal desmoplastic small round cell tumor (DSRCT) is a recently described, rare neoplasm that usually occurs in male adolescents, has a poor prognosis, and displays a typical clinicopathological profile. This aggressive neoplasm exhibits a predominantly intra-abdominal serosal pattern, with frequent pelvic extension, less frequent retroperitoneal involvement, and rare pulmonary and mediastinal spread. We report on the autopsy findings of a 9-year-old male who presented with a biopsy-proven DSRCT involving the abdomen, retroperitoneum, and scrotum and additional radiologic studies suggesting vertebral, hepatic, and mediastinal involvement. Postmortem examination performed 10 months after presentation confirmed the initial radiologic findings and demonstrated extensive pleural and pulmonary metastases and, for the first time, direct evidence of bone marrow involvement. This tumor exhibited the typical immunophenotype previously reported for DSRCT, namely multidirectional expression of epithelial, neural, and muscular markers.