Schistosomiasis & Colorectal Cancer
Chronic intestinal schistosomiasis is considered to be a risk factor for colorectal carcinoma in some parts of Asia and Africa. Both S. japonicum and S. mansoni cause intestinal schistosomiasis. In the Far East, there is considerable evidence supporting an etiological link between S. japonicum and colorectal cancer. However, the available data regarding a role of S. mansoni in colorectal carcinogenesis is not as convincing. Schistosomes are digenetic blood-dwelling flukes of the flatworm variety. Adult worms of S. japonicum and S. mansoni reside in pairs in the mesenteric vessels, where they lay their eggs. The eggs penetrate the intestinal wall and cause severe inflammatory reaction in the mucosa and submucosa. They can cause formation of granulomas, mucosal ulceration, microabscesses, polyposis, and eventually carcinogenesis through a complex interplay of many different poorly-understood processes and pathways. In this image, a few schistosome ova are seen in the stroma in between malignant glands of a well-differentiated colonic adenocarcinoma. Note the presence of numerous eosinophils within the inflammatory infiltrate.