Primary Epithelioid Angiosarcoma of the Colon With Peritoneal Carcinomatosis.

Angiosarcoma is a rare mesenchymal tissue neoplasm, typically involving lymphatic or vascular endothelial cells. The tumor can arise anywhere in the body, though it is most often found as cutaneous lesions in the head and neck region. Due to its rarity, a diagnosis can sometimes be missed, especially when the sarcoma involves an uncommon site like the gastrointestinal tract. In this case, we describe a male patient who was found to have primary epithelioid angiosarcoma of the colon. Initial biopsies with immunohistochemistry staining were weakly positive for anti-cytokeratin (CAM 5.2) and negative for SRY-Box transcription factor 10 (SOX-10) and B-cell-specific activator protein (PAX-5). He was misdiagnosed as having poorly differentiated carcinoma as a result. However, a more in-depth look at the colon specimen after tumor resection revealed CD-31 and factor VIII positivity, which established the diagnosis of epithelioid angiosarcoma of the colon. This case suggests the use of rare histopathology markers as part of the workup for colonic lesions to confirm the diagnosis, especially when tissue biopsy is limited.