Desmoplastic Small Round Cell Tumor: The Value of Cytology, Immunohistochemistry, and Molecular Features in the Diagnosis of This Challenging Diagnostic Entity

Desmoplastic small round cell tumor is a rare malignant neoplasm that usually occurs in adolescents and young adult males and typically presents as a large, often multinodular, intra-abdominal mass. The peritoneal cavity is the most common location of the tumor with multiple satellite nodules often noted at presentation. Extra-abdominal locations, such as the lung, kidney, middle ear, stomach, pancreas, pleura, bone, and the central nervous system, have been described. Distant metastases commonly involve the lymph nodes, liver, and lungs. Desmoplastic small round cell tumor is relatively rare, and only few cytologic descriptions are available. We present the case of a 16-year-old boy with unusually rapidly fatal desmoplastic small round cell tumor of the peritoneum with emphasis on the cytologic features. Recent advances in imaging techniques have resulted in increased number of cytologic preparations from unusual tumors or tumors in unusual locations. Morphologically, these tumors often display a divergent phenotype and immunophenotype. Immunohistochemistry plays a pivotal role in the characterization of these tumors and discrimination from other mimickers, particularly other “blue cell tumors.” Once suspected, identification of the characteristic translocation in these tumors confirms the diagnosis. Therefore, awareness of the cytologic features and the divergence of the immunophenotype of this tumor are crucial in order to arrive to the correct diagnosis and to ensure proper management plans of these often difficult-to-treat tumors.