Familial adenomatous polyposis is a rare inherited condition that causes hundreds to thousands of abnormal growths called polyps to develop in the colon and rectum, often during the teenage years. Without treatment, these polyps are almost certain to become cancerous by middle age, making early detection and preventive surgery essential for those affected.
Understanding the Numbers: Who Gets Familial Adenomatous Polyposis
Familial adenomatous polyposis, often referred to as FAP, affects approximately 1 in every 8,000 to 8,500 people worldwide. This makes it a rare condition, though it is one of the most well-studied hereditary cancer syndromes. The condition affects males and females equally, showing no preference for one sex over the other. Despite its rarity, FAP has a significant impact because it accounts for about 0.5 percent of all colorectal cancer cases diagnosed each year.[1][2]
The condition does not discriminate by ethnicity or geographic location, appearing across all populations and regions. However, because it is hereditary, families with a history of FAP will see multiple members affected across generations. It is estimated that between 5% and 10% of all FAP cases involve the less severe variants, such as attenuated FAP or other subtypes like Gardner syndrome and Turcot syndrome.[2]
Age plays a crucial role in the development of FAP. Polyps begin to appear in childhood or adolescence, with approximately 15% of people with FAP developing polyps by age 10, 50% by age 15, and 75% by age 20. By the time someone with untreated FAP reaches their mid-thirties, the likelihood that polyps are present approaches 95%. Without surgical intervention, the vast majority of people with FAP will develop colorectal cancer, with the average age of cancer diagnosis being around 39 years in classic FAP.[1][11]
What Causes Familial Adenomatous Polyposis
Familial adenomatous polyposis is caused by mutations in a gene called the adenomatous polyposis coli or APC gene. This gene is located on chromosome 5 and plays an important role as a tumor suppressor gene, which means it normally helps prevent cells from growing and dividing too quickly or in an uncontrolled way. When the APC gene is working properly, it produces a protein that helps regulate cell growth and keeps the development of polyps in check.[4][5]
When a mutation occurs in the APC gene, the protein it produces is abnormal and often shortened. This faulty protein cannot perform its normal function of controlling cell growth. As a result, cells in the lining of the colon and rectum begin to grow without proper regulation, leading to the formation of many polyps. These polyps are initially benign, meaning they are not cancerous, but over time they have a very high likelihood of transforming into colorectal cancer if not removed.[5]
Most people with FAP inherit the mutated gene from one of their parents. Since FAP follows an autosomal dominant pattern of inheritance, only one copy of the altered gene is needed to cause the condition. This means that if one parent has FAP, each child has a 50 percent chance of inheriting the mutation and developing the condition themselves. However, in about 25 to 30 percent of cases, the genetic mutation occurs spontaneously, meaning it happens for the first time in that individual without being passed down from a parent. This is called a de novo mutation.[1][4]
Because FAP is a genetic condition, it cannot be caused by lifestyle factors, environmental exposures, or infections. The mutation is present from birth, even though symptoms may not appear until later in childhood or adolescence. Understanding that FAP is rooted in genetics is essential for families, as it underscores the importance of genetic testing and counseling for at-risk relatives.
Risk Factors and Who Should Be Concerned
The primary risk factor for developing familial adenomatous polyposis is having a family history of the condition. If a parent, sibling, or child has been diagnosed with FAP, the risk of inheriting the same genetic mutation is significantly elevated. In families where FAP is known to exist, each child of an affected parent has a 50 percent chance of inheriting the condition. This makes family history the most important predictor of risk.[1]
People who have a known family history of FAP should undergo regular screening starting in childhood, typically around age 10 to 12 years. Early and consistent monitoring allows doctors to detect polyps as soon as they begin to form, which is critical for preventing cancer. Children in affected families are encouraged to have annual sigmoidoscopy, a procedure that uses a flexible tube to examine the lower part of the colon and rectum.[7]
While FAP itself is not influenced by lifestyle choices like diet, smoking, or physical activity, these factors can still play a role in overall colon health and may influence how aggressively polyps develop or how quickly they progress. However, no amount of healthy living can prevent FAP in someone who carries the genetic mutation. The condition is determined entirely by genetics, not by personal behavior or environmental factors.
Certain related genetic syndromes, such as Gardner syndrome and Turcot syndrome, are considered subtypes of FAP. These conditions involve the same APC gene mutations but present with additional features, such as tumors in other parts of the body or abnormalities in bones, skin, or teeth. People with these syndromes face the same high risk of colorectal cancer as those with classic FAP.[2]
Recognizing the Symptoms
The main sign of familial adenomatous polyposis is the development of hundreds to thousands of polyps in the colon and rectum. These polyps are abnormal tissue growths that appear on the inner lining of the large intestine. In most cases, polyps begin to form during the teenage years, though they can appear earlier or later depending on the individual. The sheer number of polyps is what distinguishes FAP from other conditions that may cause only a few polyps to develop over time.[1]
Many people with FAP do not experience noticeable symptoms in the early stages, especially when polyps are small and few in number. However, as polyps grow larger and more numerous, symptoms often begin to appear. One of the most common symptoms is rectal bleeding, which may show up as bright red blood in the stool or on toilet paper. This occurs because polyps can bleed, especially when they become inflamed or irritated by the passage of stool.[19]
Abdominal pain is another symptom that can occur as polyps increase in size and number. The pain may be cramping or dull and can result from polyps partially blocking the intestine or causing inflammation in the colon. Some people also experience chronic diarrhea, which happens when the large number of polyps interferes with the normal function of the colon in absorbing water and forming solid stool.[19]
Other symptoms may include unexplained weight loss, fatigue, and signs of anemia such as paleness or feeling weak and tired. Anemia can develop when chronic bleeding from polyps leads to a loss of red blood cells over time. Some individuals may also notice changes in bowel habits, such as constipation or a feeling that the bowel does not empty completely.[19]
Because FAP can also affect other parts of the body, some people develop polyps in the upper part of the digestive tract, particularly in the duodenum, which is the first section of the small intestine. These polyps can cause symptoms such as nausea, vomiting, or discomfort in the upper abdomen. In rare cases, people with FAP may develop non-cancerous growths in other areas, such as the skin, bones, or soft tissues, or they may have dental abnormalities.[1][5]
In some individuals, particularly those with attenuated FAP, symptoms may not appear until later in adulthood. Attenuated FAP is a milder form of the condition in which people develop fewer polyps, typically between 20 and 100, and these polyps tend to appear later in life. As a result, symptoms may not become noticeable until middle age, and the risk of cancer, while still high, develops more slowly.[1]
Can Familial Adenomatous Polyposis Be Prevented?
Because familial adenomatous polyposis is caused by an inherited or spontaneous genetic mutation, the condition itself cannot be prevented. However, the serious complications of FAP, particularly the development of colorectal cancer, can be prevented or significantly delayed through early detection, regular monitoring, and timely medical intervention.
For individuals who are known to be at risk because of a family history of FAP, the most important preventive measure is genetic testing. A simple blood test can determine whether someone carries the APC gene mutation. This test is especially valuable for children and young adults in families where FAP has been diagnosed. Genetic testing allows at-risk individuals to know their status early and to begin appropriate screening and surveillance before polyps develop into cancer.[7]
Once a person is diagnosed with FAP, whether through genetic testing or the appearance of polyps, regular screening becomes essential. For those with a confirmed diagnosis, annual colonoscopy examinations are recommended starting around age 10 to 12. During a colonoscopy, a doctor uses a flexible tube with a camera to examine the entire colon and rectum. This allows for the detection of polyps and, in some cases, the removal of small polyps during the same procedure.[7][12]
In most cases, surgical removal of the colon, called a colectomy, is recommended to prevent colorectal cancer. This surgery is typically performed in the late teenage years or early twenties, once polyps have developed but before cancer has had a chance to form. There are different types of colectomy, and the choice depends on the severity of polyps in the rectum. Some people may have their entire colon and rectum removed, while others may have the colon removed but the rectum preserved if it has fewer polyps. The surgeon often creates a new internal reservoir using a portion of the small intestine, which allows the person to pass stool normally after the procedure.[4]
Even after surgery to remove the colon, individuals with FAP must continue regular screening. Polyps can still develop in the remaining parts of the digestive tract, such as the duodenum or stomach, and there is an increased risk of other types of cancer. Regular upper endoscopy examinations are recommended to monitor the upper digestive tract for polyps and to remove them if they are found. Depending on the number and type of polyps, these exams may be needed every one to three years.[7][12]
In addition to surgery and screening, some medications have been studied for their potential to reduce the number and size of polyps in people with FAP. Drugs such as sulindac and celecoxib, which are types of anti-inflammatory medications, have shown some benefit in shrinking polyps. However, these medications are not sufficient on their own to prevent cancer and are not considered a substitute for surgery. They may be used in specific situations to help manage polyps, but their use must be carefully supervised by a doctor.[12]
For people who do not have a family history of FAP but are concerned about their risk of colorectal cancer in general, maintaining a healthy lifestyle can support overall colon health. This includes eating a diet rich in fruits, vegetables, and whole grains, limiting red and processed meats, staying physically active, avoiding tobacco, and limiting alcohol consumption. While these measures will not prevent FAP in someone with the genetic mutation, they are important for general cancer prevention and overall well-being.
How Familial Adenomatous Polyposis Changes the Body
Familial adenomatous polyposis brings about significant changes in the normal structure and function of the colon and rectum. In a healthy person, the lining of the colon is smooth and absorbs water from digested food, forming solid waste that is eventually eliminated. The cells in this lining grow, divide, and die in a controlled and orderly way. However, in someone with FAP, the mutation in the APC gene disrupts this normal process.
The APC protein normally acts as a brake on a cellular signaling pathway that promotes cell growth and division. When the APC gene is mutated, this brake fails, and the signaling pathway becomes overactive. Cells in the lining of the colon begin to grow and divide much faster than they should. This uncontrolled cell growth leads to the formation of polyps, which are small clumps of cells that protrude from the lining of the colon into the interior space where stool passes.[5]
At first, these polyps are benign, meaning they are not cancerous. However, the more polyps that form and the longer they remain in the colon, the greater the chance that some of them will undergo additional genetic changes. Over time, cells within a polyp can accumulate more mutations, eventually transforming into cancer. This process, known as the adenoma-to-carcinoma sequence, is well understood in colorectal cancer and is the reason why early removal of polyps is so critical in preventing cancer.[5]
In people with FAP, the risk of colorectal cancer is nearly 100 percent if the colon is not removed. Cancer typically develops by the time a person is in their 40s in classic FAP, though it can occur earlier or later depending on the individual. Once cancer develops, it can invade deeper layers of the colon wall and spread to nearby lymph nodes or distant organs, leading to serious health complications and a poorer prognosis.
The APC protein also plays a role in ensuring that cells divide properly and that the correct number of chromosomes are passed to new cells. When the APC protein is faulty, errors in cell division can occur, leading to additional genetic instability. This instability further increases the likelihood that cells will become cancerous over time.[5]
Beyond the colon and rectum, FAP can also cause polyps to develop in other parts of the digestive system, particularly the duodenum and stomach. Polyps in the duodenum can be especially concerning because they can develop near the ampulla of Vater, an important area where bile and pancreatic juices enter the small intestine. Polyps in this location have a higher risk of becoming cancerous, and people with FAP have an estimated 8 percent lifetime risk of developing duodenal cancer.[2]
FAP can also lead to changes in other tissues and organs. Some people develop desmoid tumors, which are non-cancerous but aggressive fibrous growths that can occur in the abdomen or abdominal wall. These tumors can cause problems by pressing on nearby organs or structures. Other changes include benign bone growths called osteomas, cysts in the skin, and abnormalities in the teeth. Some individuals also have a condition called congenital hypertrophy of the retinal pigment epithelium, or CHRPE, which are harmless spots on the retina of the eye that can be seen during an eye exam and help doctors confirm a diagnosis of FAP.[5]
People with FAP also face an increased risk of several other types of cancer beyond colorectal cancer. These include thyroid cancer, particularly a type called papillary thyroid cancer, which occurs in about 2 percent of people with FAP. There is also a small but increased risk of pancreatic cancer, liver cancer, stomach cancer, and brain or spinal tumors. In children with FAP, there is a slightly elevated risk of a rare liver cancer called hepatoblastoma.[2][4]
Because of these widespread effects, FAP is considered a systemic condition that requires lifelong monitoring and management. Even after the colon is removed, regular surveillance for polyps in the upper digestive tract and screening for other cancers remain essential parts of care. Understanding how FAP changes the body helps patients and their families appreciate the importance of early intervention, ongoing medical follow-up, and a coordinated approach to managing this complex condition.