It is estimated that 1 in 20 patients will be diagnosed with colorectal cancer or colon cancer each year. If colon cancer is caught early, patients have a much greater chance of survival. Unfortunately, often times colorectal cancer is discovered in its later stages, making it the second leading cause of cancer death in the United States. In 2018, the American Cancer Society lowered the screening age for the first colonoscopy from age 50 to 45, but those who have a family history of polyps, colon cancer, or colorectal cancer should be screened earlier as they are high risk. In part, this is because they may have a genetic condition known as familial adenomatous polyposis, known as FAP.
FAP accounts for roughly 1 percent of all colorectal cancer. If this marker is identified early enough, patients can be tested frequently for colorectal cancer, which can help boost survival rates. Read on to learn more about what FAP is, how it is diagnosed, and what treatments are available.
What is Familial Adenomatous Polyposis (FAP)?
Familial adenomatous polyposis is a condition inherited through genetics. The “F” in FAP denotes it as a familiar (family) condition, while the “A” for adenomatous refers to the type of polyps found in the colon. “P” for polyposis refers to the number of polyps found in the colon. Those who have polyposis have an unusually large number of colorectal polyps, even compared to those who have colorectal cancer. Polyps are the precursor to the development of colon cancer, which is by adenomatous polyposis is a concerning find. Those who have FAP have the APC gene, which is found on the long arm of chromosome 5 and follows an autosomal dominant inheritance pattern.
Polyposis refers to hundreds to thousands of polyps that develop in the colon and/or rectum, and the condition can begin as early as the teenage years. Having FAP leads directly to the development of colon cancer; as polyps are the precursor to cancer, having the FAP gene means the patient will develop colon cancer, often by age 40, with rare exceptions. The standard treatment for FAP is surgery and colon removal; however, the APC gene is present in all cells in the body. This means that polyps and growth can appear in or on other organ systems. This can include the duodenum (duodenal tumors), the eyes (congenital hypertrophy of the retinal pigment epithelium, known as CHRPE), the thyroid, bones, and abdomen (desmoid tumors). FAP patients may also experience dental abnormalities, such as extra teeth.
Familial Adenomatous Polyposis Symptoms
Symptoms of FAP may mimic other gastrointestinal disturbances, and many patients do not experience symptoms until they already have numerous growth of polyps or colorectal cancer is present. In addition, about 30 cases of FAP, while still technically inherited, are a spontaneous mutation. This means that there is no indication of polyps or colorectal cancer in the family history, so these patients are not urged to procure the genetic testing that will discover FAP. Unfortunately, these patients may not have an early diagnosis and may not see symptoms until middle- or late-stage colorectal cancer has already developed. Common FAP symptoms include:
- Change in bowel habits
- Abdominal pain
- Bleeding from the rectum
- Unexplained weight loss
- Low blood counts
These symptoms are also present in many other gastrointestinal conditions and may not immediately be cause for alarm. However, the best rule of thumb is to contact your physician if these types of symptoms persist for more than several days. While a diagnosis of FAP is rare, these symptoms could be indicative of everything from ulcerative colitis to colorectal cancer.
How Is FAP Diagnosed?
Diagnosis for FAP is initially based upon family history. Roughly 60 to 70 percent of patients who carry the FAP gene inherited it from a parent. These cases have polyps, colorectal cancer, or colon cancer present in the immediate family history. If your mother or father has a history of colon cancer or polyps, you should always let your doctor know, as there is a risk of having FAP.
The first step of genetic testing for FAP is a simple blood test, which looks for the FAP gene mutation. In a majority of cases (80 percent), the APC gene mutation is easily detectable with this blood test. However, 20 percent of FAP cases cannot be detected with the blood test. The test can only look for the gene mutation and is not indicative of the presence of polyps or cancer. If the gene mutation is not found via the blood test, yet the physician and patient want to rule out a FAP diagnosis completely, more invasive testing is needed.
The genetic test involves either a DNA sequencing or a protein truncation test. Often, family members who have had polyps or colorectal cancer are tested first to make sure that the gene mutation is present. If it is not, then a blood test will not likely find the gene mutation in the patient being tested. FAP testing should only be performed and evaluated by gene specialists who are knowledgeable in the field, as this type of gene testing is very complicated.
If the blood test does not show FAP, but it is still suspected, a thorough examination of the colon is needed. A colonoscopy is the primary way to detect colon cancer, but the physician may not deem it the best next step in detecting FAP. He or she may want a different type of scope test, known as sigmoidoscopy, which uses a sigmoidoscope. This shorter scope examines just the first one to two feet of the colon and is not as invasive or thorough as a colonoscopy. Since the physician is looking for FAP and not colon cancer necessarily, a colonoscopy may not be warranted.
A colonoscopy is also a viable way to determine if FAP is present, but requires more preparation. During a colonoscopy, the patient is usually sedated and would need a friend or family member to drive them home. Part of why the colonoscopy is a good choice is because the colonoscope can both detect and remove cancerous polyps. However, in the case of polyposis, this may not be possible.
Are There Subtypes of FAP?
There are several different diagnosable subtypes of FAP, which patients may want to make themselves familiar with if they have concerns. The subtypes include:
- Classic FAP is the most common type of FAP, and typically, the best way to treat it is to have a colectomy (removal of the colon) because of the sheer number of polyps present.
- Attenuated FAP (known as AFAP) is associated with the development of 20 to 100 polyps. This type of FAP predisposes a patient to colorectal cancer if the polyps are not removed in time. While a colectomy is typically not a treatment for AFAP, patients must be carefully monitored throughout their lifespan to ensure that classic FAP does not develop.
- Gardner syndrome is a FAP variant. Those with Gardner syndrome develop adenomatous colon polyps but other problems as well, which may include epidermoid cysts (lumps on or under the skin), osteomas (lumps on or in the bone), fibromas (fibrous tumors), and desmoid tumors (tumors that may develop anywhere in the body).
- Turcot syndrome is another FAP variant. These patients develop polyps, but also have a predisposition to the development of brain tumors. Turcot syndrome is also considered a variant of Lynch syndrome.
FAP Treatment and Outlook
Because of the sheer number of polyps a patient with FAP has, they cannot be removed individually, such as with a colonoscopy. Therefore, more serious action is required. Complete removal of the colon is typically required. Options include total colectomy and ileorectal anastomosis (IRA), which is an option for patients with very few polyps in the rectal area; colectomy with ileoanal pouch (restorative proctocolectomy), which removes both the colon and the rectum; and proctocolectomy and ileostomy, which is an option for patients with existing rectal cancer.
Recovery time usually involves four to six weeks after surgery, but most patients return to their daily lives with normal activity levels and regular eating habits. Doctors may also prescribe medications, such as sulindac, which helps shrink polyps post-surgery and can help prevent their return. While the colon or rectum may be removed, polyps can still reform in other areas and in turn, cause cancer. As long as polyps are prevented from returning, the outlook for FAP post-surgery is reassuring when it comes to the development of cancer.
If you need more information about FAP or genetic testing or wish to be examined, request an appointment with Dr. Sameer Islam today. Dr. Islam’s experience and knowledge and caring support staff help provide better patient experiences that overall better maintain patient health.