Without colectomy, the prognosis for individuals with FAP is very poor. Patients who have not undergone colectomy develop colorectal cancer at an average age of 39 years. The majority of untreated people die from colorectal cancer by the age of 42 years. For those who do undergo a colectomy, prognosis is variable, depending on development and progression of other tumors. For example, desmoids can also be detrimental to those affected with FAP, accounting for 11–31% of all mortality in these individuals.
King, John E., Roger R. Dozois, Noralane M. Lindor, and David A. Ahlquist. "Care of Patients and Their Families With Familal Adenomatous Polyposis." Mayo Clinic Proceedings 75, no. 1 (January 2000): 57–67.
Lynch, Henry T., and Thomas C. Smyrk. "Hereditary Colorectal Cancer." Seminars in Oncology 26, no. 5 (October 1999): 478–484.