Arch Pathol Lab Med—Vol 124, October 2000 Pathologic Quiz Case—Mathur & Schwartz 1561 Pathologic Quiz Case A 33-Year-Old Man With an Abdominal Mass Sharad C. Mathur, MD; Arnold M. Schwartz, MD, PhD A 33-year-old African-American man presented with a 3-week history of back pain, shortness of breath, cough, fevers, and vomiting. He had experienced a 20-lb weight loss and complained of constipation for 4 days prior to admission. His past medical history was signiﬁcant for an upper gastrointestinal bleed secondary to a duodenal ulcer 4 weeks prior to admission. He was hypertensive and carried the sickle cell trait. He had a 16-pack-year smoking history and drank a 6-pack of beer a day. On admission, his vital signs were stable. He was in mild distress and had a distended abdomen with no palpable organomegaly. Coarse breath sounds were heard over the right lower chest, and that area was also dull to percussion. A computed tomographic scan showed bilateral pleural effusions (greater on the right side), a 2.5-cm left lower lobe lung nodule, multiple low-density liver lesions, mul- tiple retroperitoneal nodules with involvement of the right kidney with hydronephrosis, a large inferior vena cava thrombus, and evidence of small bowel obstruction. Lab- oratory values were signiﬁcant for a white blood cell count of 26.4  10 9 /L with 0.93 neutrophils, 0.03 lymphocytes, and 0.03 monocytes; a platelet count of 939  10 9 /L; se- Accepted for publication November 23, 1999. From the Department of Pathology,The George Washington Univer- sity Medical Center, 901 23rd St NW, Washington, DC 20037. Reprints not available from the author. rum urea nitrogen, 6.8 mmol/L; and creatinine, 115 mol/L. Urinalysis showed trace protein and rare white cells but no blood. The patient was started on heparin, and a percutaneous, ultrasound-guided needle core biopsy of the retroperitoneal mass was performed. Touch imprints from the needle core biopsy showed clusters of large malignant cells with well-deﬁned cyto- plasmic borders, hyperchromatic nuclei, slightly irregular nuclear contours, and prominent nucleoli (Figure 1). A subsequent pleural ﬂuid specimen showed malignant cells with similar cytologic features. The biopsy showed sheets and cords of large epithelioid cells with abundant eosin- ophilic cytoplasm and enlarged hyperchromatic nuclei with conspicuous nucleoli (Figure 2, A, low power, origi- nal magniﬁcation 25; B, high power, original magniﬁ- cation 100). There was a small amount of intervening stroma with neutrophils. Areas of necrosis were present. The tumor cells were positive for keratins (CAM 5.2, AE1/ AE3) and vimentin, but negative for S100 protein and lym- phoid markers (leukocyte common antigen, CD20) by im- munohistochemical staining. Transmission electron mi- croscopy demonstrated large tumor cells with irregular nuclei, streaming bundles of cytokeratin, and varying amounts of rough endoplasmic reticulum, mitochondria, and lysosomes (Figure 3). No intercellular junctions were seen. No glandular or endocrine features were identiﬁed. What is your diagnosis?