CASE REPORT Desmoplastic Small Round Cell Tumor: A Rare Case of Extraluminal Bowel Obstruction and Review of the Literature Emmanuel Ofori 1 & Daryl Ramai 1 & Sofia Nigar 1 & Philip Xiao 2 & Gullamulah Shahzad 1 & Madhavi Reddy 1 # Springer Science+Business Media, LLC, part of Springer Nature 2017 Introduction Desmoplastic small round cell tumor (DSRCT) is an extreme- ly rare malignant neoplasm that was first described by Sesterhenn et al. [1]. Its estimated incidence is between 0.2 and 0.5 per million per year [2]. DSRCT has been character- ized as a highly aggressive cancer, which predominantly af- fects male adolescents and young adults. It usually presents as multiple widespread peritoneal and omental implants within the abdomen and pelvis [3]. Peritoneal metastasis is almost always present at diagnosis, and concurrent extraperitoneal metastases have been found in 47% of patients [4]. Four good prognostic factors include absence of extraperitoneal metasta- sis, macroscopic resection of peritoneal disease, whole abdominopelvic radiotherapy, and postoperative chemothera- py. Herein, we describe a 25-year-old male patient who pre- sented with constipation and abdominal distension and subse- quently diagnosed with desmoplastic small round cell tumor. Case A 25-year-old male with no known past medical history was admitted for constipation, bloating, right upper quad- rant abdominal pain, and worsening abdominal distension. He reported an associated 20 lbs, unintentional weight loss, and decreasing appetite over the prior 2 months. He admitted to occasional alcohol consumption and ciga- rette smoking. The patient denied a family history of can- cer. Physical examination was significant for a hard mass palpated in the left upper quadrant and distension of the abdomen. Heart rate was 97.6/min, blood pressure was 136/90 mmHg, respiratory rate was 20/min, oxygen satu- ration was 97% on room air, and temperature was 97.6 °F. Laboratory results were within normal limits with a white blood cell (WBC) count of 9.5/ul, hemoglobin of 13.3 g/ dl, and hematocrit of 41%, but platelet count of 586 k/ cmm. Computed tomography (CT) scan of the abdomen and pelvis revealed a moderate amount of ascites particularly in the perihepatic and perisplenic region and also within the right lower quadrant and small bowel mesentery. Innumerable individual and conglomerate masses were identified throughout the abdomen and pelvis, the largest of which was heterogeneous with areas of low density consistent with necrosis. Multiple peritoneal or omental implants were also noted along with evidence of bowel obstruction at the level of the sigmoid colon (Fig. 1). Needle biopsy of the abdominal mass revealed malig- nant epithelioid neoplasm composed of sheets and nests of small cells and slightly larger, clear cells, embedded in abundant fibrotic and desmoplastic stroma. The nu- clei were round to oval and hyperchromatic with small inconspicuous nucleoli. Immunohistochemical stains showed expression of cytokeratin (CAM5.2 and AE1/ AE3), desmin, CD99, and FLI1 and negative for WT1, S100, synaptophysin, and chromogranin (Fig. 2 ). Fluorescence in situ hybridization (FISH) assay for EWSR1-WT1 rearrangement was positive, consistent with DSRCT. The FISH analysis was conducted using a fusion probe, and the immunohistochemical staining for WT1 was carried out using clone WT49 (Leica Biosystems) against the N-terminus. Clone dilution was not required according to manufacturer ’ s instructions. * Daryl Ramai dramai@sgu.edu 1 Division of Gastroenterology and Hepatology, The Brooklyn Hospital Center, Academic Affiliate of The Icahn School of Medicine at Mount Sinai, Clinical Affiliate of The Mount Sinai Hospital, 121 Dekalb Avenue, Brooklyn, NY 11201, USA 2 Department of Pathology, The Brooklyn Hospital Center, Academic Affiliate of The Icahn School of Medicine at Mount Sinai, Clinical Affiliate of The Mount Sinai Hospital, 121 Dekalb Avenue, Brooklyn, NY 11201, USA Journal of Gastrointestinal Cancer https://doi.org/10.1007/s12029-017-0045-4