What is a common long-term complication of untreated familial adenomatous polyposis?

Familial adenomatous polyposis (FAP) is a genetic disorder characterized by the development of numerous polyps in the colon and rectum at a young age. If left untreated, these polyps have a high likelihood of progressing to colorectal cancer. The polyps typically begin to develop in adolescence or early adulthood and, without surveillance or intervention such as colectomy, virtually all individuals with FAP will develop colorectal cancer by their mid-30s to early 40s.

The cancer arises from the adenomatous polyps present in the colon, underscoring the importance of early diagnostic practices and surgical recommendations to mitigate cancer risk. Thus, the long-term complication most directly associated with untreated FAP is indeed colorectal cancer, making it the most pertinent answer in this context. The other cancers listed, while possible in certain contexts, are not directly associated as common long-term complications of FAP itself.