What is familial adenomatous polyposis (FAP)?

What FAP is

FAP is an inherited disorder that greatly raises the risk of cancer of the colon and rectum, according to MedlinePlus Genetics from the U.S. National Library of Medicine. It is caused by variants in the APC gene. That gene normally makes a protein that keeps cells from growing and dividing too fast. When the protein does not work, cell growth is not controlled, and polyps form.

The condition is passed down in an autosomal dominant pattern. That means one altered copy of the gene is enough to cause it. An affected parent has a 50% chance of passing the variant to each child. MedlinePlus puts the incidence at 1 in 8,500 people.

There are two forms:

• Classic FAP: polyps can start in childhood and may number in the hundreds to thousands. At least 90% of people develop colorectal cancer by age 50 unless the colon is removed first.
• Attenuated FAP: fewer polyps, about 30 on average, that appear later in life. The lifetime colorectal cancer risk is 70%.

Why the upper gut matters

FAP also affects the upper gut. Duodenal adenomas are polyps in the first part of the small intestine. They are found in 80% to 100% of people with FAP, says the National Cancer Institute. It says 4% to 12% of people with FAP develop duodenal cancer in their lifetime.

Doctors usually start checking the duodenum by endoscopy between ages 20 and 25. The Spigelman stage, a grade for how severe the polyps are, often sets how often checks are repeated. Removing duodenal polyps by endoscopy can cause complications, mainly pancreatitis, bleeding or a tear in the duodenum. Drugs such as celecoxib and sulindac have been linked to smaller and fewer polyps in studies, NCI notes. It adds that no drug is currently FDA-approved to prevent polyps or cancer in FAP.

Where AI comes in

Recursion is testing REC-4881, a pill that blocks the proteins MEK1 and MEK2, in FAP. The company says AI-driven screens of cells pointed it to the drug. Its TUPELO trial enrolls adults with FAP who have had all or part of the colon removed. On October 15, 2026, Recursion reported that 13 of 15 patients had less total polyp burden after 12 weeks. These are company-reported results from a small, single-arm study. Recursion says FAP has no approved drug therapy.