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Hereditary Cancer and Genetic Testing

Cancer risks in people with an inherited APC mutation
 

Familial adenomatous polyposis (FAP) and atypical familial adenomatous polyposis (AFAP)

Without surgery, almost all people with FAP will develop colorectal cancer in their lifetime, often before age 40. The estimated lifetime cancer risks for people with FAP are listed below. People with the attenuated form of FAP (AFAP) may have lower lifetime risks for cancer, and the degree of risk depends on the severity of their polyp history. Importantly, these risks do not apply to people who have the specific APC variant I1307K. See below for the specific cancer risks in people with that variant. 

   

Risk for cancer in people with FAP. Source: NCCN Guidelines: Genetic/Familial High-Risk Assessment: Colorectal, vs. 1 2022.  
Cancer type Estimated lifetime risk
(to age 80) with FAP
Average lifetime risk in the general population Average age of onset with FAP
Colon cancer without colectomy Close to 100%  4.1% 39 years (median)
Colon cancer after colectomy
  • Rectal cancer with IRA surgery: 10-30%
  • Pouch and ATZ/rectal cuff after IPAA surgery: 1-3%
 
  • 46-48 years
  • Unknown
Duodenum or periampullary cancer <1-10%   50-52 years
Gastric 0.1-7.1% 0.8% 52-57 years
Small bowel cancer (beyond the duodenum) <1% 0.3% 43 years
Thyroid (mostly papillary thyroid carcinoma) 1.2-12%  1.2% 26-44 years
Intra-abdominal desmoid tumors 10 - 24% (more common with mutations at the 3' end of the gene) Rare 31-33 years
Pancreatic 1-2% 1.7% 52 years
Brain/CNS (mostly medulloblastoma) 1% 0.6% 18 years
Hepatoblastoma 0.4-2.5% (usually before age 5) Very rare 18-33 months

 

APC variant I1307K

People with an I1307K variant in the APC gene do not develop FAP. Unlike people with FAP, people with the APC variant I1307K have only a slightly elevated risk for colorectal cancer above the general population. The lifetime risk for colorectal cancer with this variant is estimated to be about 8-10%. The I1307K variant is not known to increase risk for other cancers.

 

Last updated February 08, 2022