Attenuated Familial Adenomatous Polyposis

What is Familial Adenomatous Polyposis (FAP)?

FAP is an inherited colorectal cancer syndrome and accounts for 1 percent of all cases of colorectal cancer. The “F” stands for familial, meaning it runs in families; “A” stands for adenomatous, the type of polyps detected in the colon and small intestine that can turn into cancer; and “P” stands for polyposis, or the condition of having lots of colon polyps. The gene for FAP is on the long arm of chromosome 5 and is called the APC gene.
Patients with FAP develop hundreds to thousands of colon polyps, usually starting in the teens. All patients will develop colorectal cancer from the colon polyps usually by age 40. Patients with FAP must have the colon, and sometimes the rectum, removed to prevent colon cancer.
Since the abnormal gene that causes FAP is present in all of the body’s cells, other organs may develop growths.

In over 80 percent of patients with FAP, polyps form in the stomach and small intestine. The polyps found in the upper portion of the stomach are called fundic gland polyps. Some patients have none, while others may have a carpeting of these polyps. These polyps should be biopsied once to confirm their microscopic makeup. Fundic gland polyps do not turn into cancer and usually do not require any special treatment.
The polyps found in the bottom of the stomach (the antrum) most often are precancerous polyps called adenomas. They should be biopsied to confirm and completely removed because of the risk of cancer.

Polyps in the duodenum (the first part of the small intestine) are adenomas and can turn into cancer also. In fact, duodenal cancer is the second leading cause of cancer deaths in patients with FAP, once the colon has been removed. The overall risk of duodenal cancer in FAP is about 4%. If patients have severe or advanced duodenal polyposis, the risk can be as high as 25%. Duodenal polyps can be very subtle and hard to detect, or they may be obvious and cover a large segment of the duodenum. They are often found at the opening of the bile duct and the duodenum, called the papilla. Because of the great number of polyps, they are usually not removed. However, they need to be checked regularly for the remainder of the patient’s life. Biopsy of any large or concerning duodenal polyps and the papilla, even if the papilla appears normal, should be performed regularly.

The other organs that form tumors include the skin, bones, eye (congenital hypertrophy of the retinal pigment epithelium CHRPE); thyroid and abdomen (desmoid tumors). Extra teeth may also form in patients with FAP.
Gardner’s syndrome and FAP are due to an inherited mutation in the APC gene. Attenuated FAP is a variant of FAP where there are fewer polyps in the colon. The colorectal polyps and cancer in attenuated FAP usually occur later in life than in FAP; however, the risk of colon cancer and upper gastrointestinal polyps is the same as in FAP.

How is FAP Diagnosed?

Family History
The first step in making the diagnosis of FAP is based upon the family history of colorectal polyps and cancer. The majority (60 percent to 70 percent) of patients with FAP have inherited the gene from one of their parents. Therefore, consecutive generations may have FAP. Taking a careful family history is crucial in diagnosing FAP.
In about 30 percent of FAP patients, the abnormal gene was produced at the time of conception. In these patients, no family history of FAP would be found. All of the next generations are at risk of inheriting the newly mutated gene.

What is the treatment when polyposis is found?

Surgery

Since colonic polyps form by the hundreds and thousands in FAP, they cannot be removed individually. Surgical removal of the colon is the only effective treatment. While the thought of having surgery may be upsetting, it must be done to prevent colon cancer from forming.
Polyps begin forming as young as puberty. When polyps are detected, a colorectal surgeon should be involved in the care of the patient to help guide the timing of surgery. There have been advances in the way that operations are performed. Depending on the situation, any of the following operations may be performed with the aid of small holes in the abdomen called laparoscopy or through the standard abdominal incision called laparotomy.

The most common surgical treatments are:

Total colectomy and ileorectal anastamosis (IRA)

Patients with few polyps in the rectum usually undergo this procedure. During the operation, the surgeon removes the patient’s colon but leaves 5 inches of the rectum. The small intestine, or ileum, is then surgically joined to the upper rectum. Afterward, the patient has normal bowel function.

Colectomy with ileoanal pouch (restorative proctocolectomy)

This surgical procedure is successful in selected FAP patients. The surgeon removes the colon and the rectum, leaving the anal canal and the anal sphincter muscles. A new rectum is made from the small intestine and attached to the anal canal. Sometimes a temporary opening in the abdomen, called an ileostomy or stoma, is created. After the first operation has healed, the ileostomy is closed, restoring normal bowel function.