Purpose: We report a patient with rectosigmoidal adenomatous polyposis.
Methods: A 57-year-old male presented with a submucosally invasive well-differentiated adenocarcinoma in the rectum and approximately 100 adenomatous polyps with an extremely unusual distribution limited exclusively to the rectum and sigmoid colon.
Results: There was no family history of colorectal disease or any related disorders. No extracolonic manifestations were found. Because this case was considered to be a discriminative phenotype of familial adenomatous polyposis, DNA from a peripheral sample of whole blood was screened for APC germline mutation by a combination of protein truncation test and single stranded conformation polymorphism, but no mutation was found.
Conclusion: This patient may have a novel entity of adenomatous polyposis with a peculiar distribution. It may be caused by some genetic alteration other than APC mutation.