What Is Rectal Cancer?

Rectal cancer begins when cells in the rectum—the final portion of the large intestine—start to grow and divide abnormally. The rectum is the last six to eight inches of the large intestine, positioned between the colon and the anus. This part of your digestive system stores waste material before it leaves your body.^[1]

Most rectal cancers start as small clumps of abnormal cells called polyps, which are growths on the inner lining of the rectum. These polyps, particularly the type known as adenomas, are usually harmless at first. However, over time, some can transform into cancer. This process is typically slow, often taking between 10 to 15 years for a polyp to become cancerous.^[2]

While rectal cancer and colon cancer share many similarities and are often discussed together under the term colorectal cancer, they require different treatment approaches. This difference is mainly because the rectum sits in a tight space within the pelvis, closely surrounded by other organs and structures, making surgical removal more complex.^[1]

Epidemiology: Who Gets Rectal Cancer?

Rectal cancer is a significant health concern around the world. It is the second most common cancer in the large intestine, with colorectal cancers overall being the second most common cancers in humans and a major public health problem worldwide.^[5] In the United States, rectal cancer is the third most common cancer in the digestive system, following colon cancer and pancreatic cancer. Experts estimate that about 46,200 people will receive a rectal cancer diagnosis in 2024.^[2]

It is estimated that colon and rectal cancers combined will see 151,030 newly diagnosed cases in 2022, with an estimated 52,580 deaths. The lifetime risk of developing colon or rectal cancer for any individual is approximately 4.1 percent.^[6]

While older age is a main risk factor for most cancers, there has been a noticeable trend in recent years toward earlier age at diagnosis. The average age of diagnosis is 63, yet an increasing number of younger people are being diagnosed with rectal cancer. This shift has led to changes in screening recommendations, with the recommended age to start screening now lowered to 45 years old.^[2][6]

Men are slightly more likely to develop rectal cancer than women. Statistically, people who are Black are more likely to develop rectal cancer, although the reasons for this disparity are not fully understood yet.^[2]

Causes of Rectal Cancer

The exact cause of rectal cancer remains unknown. However, scientists understand that colorectal cancer is caused by certain changes in how colorectal cells function, particularly in how they grow and divide into new cells. These changes are often linked to damage in the DNA of cells.^[3]

Most rectal cancers begin as polyps on the inner lining of the rectum. Over many years, these polyps can undergo changes that turn them into cancerous tumors. Because the transformation from a polyp to cancer is typically slow, there is often a window of opportunity for detection and removal before cancer develops.^[2]

Risk Factors for Rectal Cancer

A risk factor is anything that increases your chance of getting a disease. Some risk factors can be changed, such as lifestyle habits, while others cannot, such as your age or family history. Having one or more risk factors does not guarantee you will develop rectal cancer, and many people with no known risk factors can still get the disease.^[3]

The risk of rectal cancer increases with age, and older age is a main risk factor for most cancers. The chance of getting cancer increases as you get older. Even though age is beyond your control, understanding other risk factors can help you make informed choices about your health.^[3]

Having a biological family history of rectal cancer significantly increases your risk. If you have a first-degree relative—such as a parent, sibling, or child—with a history of colon or rectal cancer, your chance of developing it is almost double. This family connection suggests that genetics and shared environmental factors may play a role.^[2][3]

Certain inherited conditions, known as familial colorectal cancer syndromes, dramatically increase the risk of developing rectal cancer. These syndromes include Lynch syndrome (also called hereditary nonpolyposis colorectal cancer), familial adenomatous polyposis (FAP), MUTYH-associated polyposis (MAP), juvenile polyposis syndrome (JPS), Peutz-Jeghers syndrome, and PTEN hamartoma tumor syndrome. These are caused by inherited changes in certain genes.^[2][3]

A personal history of colon, rectal, or ovarian cancer increases your risk of developing rectal cancer again or for the first time. Additionally, having a personal history of high-risk adenomas—colorectal polyps that are one centimeter or larger in size or have cells that look abnormal under a microscope—also raises your risk.^[3]

Certain chronic inflammatory bowel diseases, such as Crohn’s disease and ulcerative colitis, particularly if you have had them for eight years or more, can increase your risk for rectal cancer. The ongoing inflammation in the bowel lining may contribute to the development of cancer over time.^[2][3]

Lifestyle factors also play a role. People who eat a lot of red meat and processed meat have a higher risk of developing rectal cancer. Obesity is another modifiable risk factor; people who have obesity are more likely to have rectal cancer compared to people who don’t. Regular consumption of three or more alcoholic drinks per day and smoking cigarettes are both associated with increased risk. Recent research suggests that people who smoke tobacco are more likely to die from rectal cancer than people who don’t.^[2][3]

Symptoms of Rectal Cancer

Rectal cancer may not cause symptoms early on. In many cases, people can have rectal cancer for years without noticing any changes in their body. When symptoms do appear, they usually indicate that the disease has progressed. Because symptoms can also be caused by other common conditions, such as hemorrhoids or inflammatory bowel disease, it is important to see a healthcare provider for proper evaluation.^[1][2]

One of the most common symptoms of rectal cancer is rectal bleeding, which may make your stool look dark maroon or bright red in color. You might also notice blood in or with your stool. However, not all bleeding is visible; sometimes blood can only be detected through special tests.^[1][4]

Changes in bowel habits are another warning sign. This can include diarrhea, constipation, or a more frequent need to pass stool. You might also feel that your bowel doesn’t empty completely, even after using the bathroom. Some people notice that their stools become narrower or have a different shape than usual, sometimes described as looking stringy or as thin as a pencil.^[1][2]

Abdominal discomfort is also common. This can include abdominal pain, frequent gas pains, bloating, fullness, or cramps. Some people experience general discomfort in their stomach area without being able to pinpoint a specific cause.^[4]

Systemic symptoms can occur as well. Unexplained weight loss, meaning you lose weight without trying, is a potential sign of rectal cancer. You may also feel unusually tired or weak, experience a change in appetite, or notice that you feel fatigued more easily than before.^[1][2]

During a medical exam, your doctor may find a lump in the rectum. This is often discovered during a digital rectal exam (DRE), a routine procedure in which the doctor inserts a gloved finger into the rectum to feel for abnormalities.^[1]

Prevention of Rectal Cancer

While not all cases of rectal cancer can be prevented, there are several steps you can take to significantly reduce your risk. Prevention strategies focus on lifestyle changes, regular screening, and early detection of precancerous polyps.^[6]

Most colon and rectal cancers start as polyps. Rectal cancers can be prevented by discovering and removing these polyps before they turn into cancer. This is done through screening procedures, particularly colonoscopy. During a colonoscopy, a doctor can not only detect polyps but also remove them immediately. Because it usually takes years for a polyp to become cancerous, routine detection and removal greatly decrease the development of rectal cancer.^[6]

All patients should discuss recommendations for colon and rectal cancer screening with their healthcare providers. Screening for the average risk patient should begin at age 45. However, this may be different for individuals depending on personal and family health history. If you have risk factors such as a family history of colorectal cancer or inflammatory bowel disease, your doctor may recommend starting screening at a younger age.^[6][7]

Evidence suggests that dietary choices can influence your risk. A high-fiber, low-fat diet may decrease the risk of developing colon or rectal cancer. This means eating plenty of fruits, vegetables, and whole grains while limiting red and processed meats, as well as foods high in saturated fats.^[6]

Maintaining a healthy weight is also important. People with obesity are more likely to have rectal cancer, so achieving and maintaining a healthy weight through diet and physical activity can reduce your risk. Regular physical activity has been shown to have protective effects against colorectal cancer.^[2]

Limiting alcohol consumption and avoiding tobacco are also key prevention strategies. Having three or more alcoholic drinks per day increases your risk, as does smoking cigarettes. Quitting smoking and moderating alcohol intake can lower your risk not only for rectal cancer but also for many other health conditions.^[2][3]

Pathophysiology: How Rectal Cancer Develops

Understanding how rectal cancer develops in the body involves looking at the changes that occur at the cellular and tissue level. The rectum is part of your body’s digestive system. The digestive system takes in nutrients from foods and helps pass waste material out of the body. It is made up of the esophagus, stomach, and the small and large intestines. The colon makes up the main part of the large intestine and is about five feet long. Together, the rectum and anal canal make up the last part of the large intestine and are six to eight inches long.^[3]

The inner lining of the rectum is where most rectal cancers begin. This lining is constantly renewing itself, with old cells dying and new cells replacing them. When the mechanisms that control this process become damaged, cells can begin to grow and divide in an uncontrolled way, forming polyps. Not all polyps are the same; some types, particularly adenomas, have a higher chance of becoming cancerous.^[2]

Colorectal cancer is caused by certain changes to the way colorectal cells function, especially how they grow and divide into new cells. Many risk factors increase the chance of DNA damage in cells, which may lead to colorectal cancer. DNA is the instruction manual for how cells should behave. When DNA is damaged and not properly repaired, it can lead to mutations that allow cells to grow out of control.^[3]

As a polyp transforms into cancer, the cancerous cells can invade deeper layers of the rectal wall. The rectum is exposed to concentrated fecal matter in a direct way, and the undigested matter traveling through the colon is coated with alkaline mucus, leading to different levels of pH in the colon and rectum. These environmental factors may influence susceptibility to cancer development.^[5]

Once cancer develops, it can grow through the layers of the rectal wall and potentially spread to nearby lymph nodes or other organs. Because the rectum is located within the pelvic cavity and has close relationships with genitourinary organs, rectal tumors may present with special clinical manifestations different from other cancers within the gastrointestinal tract. The tight space in which the rectum sits can make surgical removal of rectal cancer complex and can affect the pathways through which cancer spreads.^[5]

The stage of the cancer—how far advanced it is at diagnosis and the extent of its spread—is generally the most important factor affecting outcomes. However, other factors can also affect outcomes, including the location of the tumor in the rectum, whether the tumor is causing a blockage of the bowel or a perforation (a hole in the rectum), as well as the patient’s general health and ability to tolerate treatment.^[6]