Sarcomatoid carcinoma in the pelvic cavity.

Sarcomatoid carcinoma in the pelvic cavity is very rare. A 58-year-old Japanese man was admitted to our hospital because of lower abdominal fullness. CT and MRI revealed a large mass in the left pelvic cavity. Transurethral bladder endoscopy showed tumor invasion, and large biopsies were obtained from the bladder lesion. Histologically, the tumor was composed of malignant round cells with hyperchromatic nuclei. Many intracytoplasmic vacuoles were present. No carcinomatous areas were seen. Immunohistochemically, the tumor cells were positive for cytokeratin (CK) 18, vimentin, p53 and Ki-67 (labeling 80%). The tumor cells were negative for panCK AE1/3, CD5/6, CK7, CK8, CK14, CK19, CK20, CK 34BE12, EMA, desmin, calretinin, WT-1, S100 protein, α-smooth muscle actin, CEA, CD34, CD45, CD20, factor VIII-related antigen, synaptophysin, p63, CDX2, and myoglobin. Because the CK18 was diffusely expressed, the pathological diagnosis was sarcomatoid carcinoma.