Rectal cancer develops when abnormal cells grow in the rectum, the last several inches of the large intestine. While this diagnosis can feel overwhelming, understanding the disease, its risk factors, and treatment options can help patients and families navigate the journey ahead with greater confidence and clarity.
Understanding Rectal Cancer and Its Patterns Across Populations
Rectal cancer forms in the tissues of the rectum, which is the final part of the large intestine extending approximately six to eight inches from the anal opening. Together with colon cancer, rectal cancer falls under the category of colorectal cancer, meaning cancers that affect the colon or rectum. Although these two types of cancer share many similarities, they are treated differently due to differences in anatomy and how the disease may spread.[1][3]
Colorectal cancer as a whole represents a significant health concern globally. Worldwide, it is the third most common form of cancer, with an estimated 1.93 million new cases and over 900,000 deaths recorded in 2022 alone. In the United States, rectal cancer accounts for a considerable portion of colorectal cancer cases. Experts estimate that approximately 46,200 to 46,950 people will receive a rectal cancer diagnosis in 2024. When combined with colon cancer, colorectal cancer is the third most commonly diagnosed cancer in the United States and the second leading cause of cancer deaths.[2][4][8][17]
Rectal cancer affects men and women in nearly equal numbers, though men have a slightly higher risk of developing the disease. The average age at diagnosis is 63 years, with the risk increasing significantly as people age. However, a concerning trend has emerged in recent years: more cases are being diagnosed in younger adults under the age of 50. This shift has led medical organizations to lower the recommended age for routine screening from 50 to 45 years.[2][8][17]
Among all racial and ethnic groups in the United States, Black individuals have the highest rates of both developing and dying from colorectal cancer. The reasons behind these disparities are complex and not fully understood, but they highlight the importance of awareness and access to screening and treatment for all populations.[3][17]
What Causes Rectal Cancer
The exact cause of rectal cancer remains unknown, but scientists understand that it develops through a series of changes in the cells lining the rectum. Most rectal cancers begin as small clumps of abnormal cells called polyps, specifically adenomas. These polyps are not cancerous when they first appear, but over time they can transform into cancer. This process typically takes between 10 to 15 years, which provides a window of opportunity for detection and removal before cancer develops.[2][4]
The transformation from normal rectal tissue to a cancerous tumor requires an accumulation of genetic mutations. These mutations can be either somatic, meaning acquired during a person’s lifetime, or germline, meaning inherited from parents. Over many years, these genetic changes cause cells to grow and divide in abnormal ways, eventually forming a tumor.[3][4]
Colorectal cancer is caused by certain changes in how colorectal cells function, especially in how they grow and divide into new cells. Many risk factors increase the chance of DNA damage in cells that may lead to colorectal cancer, but they do not directly cause cancer themselves. Instead, they increase the probability that cancer-causing mutations will occur.[3][10]
Risk Factors That Increase Your Chances of Developing Rectal Cancer
Several factors can increase a person’s risk of developing rectal cancer. Understanding these risk factors can help individuals make informed decisions about screening and lifestyle choices. Age is the most important risk factor for most cancers, including rectal cancer. The chance of developing this disease increases significantly as people get older, though recent trends show an increase in younger adults as well.[2][3]
Family history plays a crucial role in rectal cancer risk. Having a first-degree relative—a parent, sibling, or child—with a history of colon or rectal cancer nearly doubles a person’s risk of developing the disease. This increased risk may be due to shared genetic factors, environmental exposures, or lifestyle habits within families.[2][3][5]
Personal medical history also matters. Individuals who have previously had colorectal cancer, ovarian cancer, or colon polyps are at higher risk. Specifically, having high-risk adenomas—polyps that are one centimeter or larger, or that have abnormal-looking cells under a microscope—increases the likelihood of developing rectal cancer.[3][5][10]
Chronic inflammatory bowel diseases, particularly ulcerative colitis and Crohn’s disease, increase rectal cancer risk when they have been present for eight years or more. The ongoing inflammation in the intestinal lining can lead to cellular changes that eventually become cancerous.[2][3][10]
Lifestyle factors also contribute to risk. People who consume large amounts of red meat and processed meat have a higher risk of developing rectal cancer. Obesity is another modifiable risk factor—people with obesity are more likely to develop rectal cancer compared to those maintaining a healthy weight. Smoking cigarettes and consuming three or more alcoholic drinks per day have both been linked to increased rectal cancer risk.[2][3][10]
Recognizing the Symptoms of Rectal Cancer
One of the most challenging aspects of rectal cancer is that it can exist for years without causing any noticeable symptoms. In many cases, rectal cancers are discovered during routine screening rather than through symptoms. When symptoms do appear, they often indicate that the cancer has grown or advanced. However, it’s important to remember that these symptoms can also be caused by many other, less serious conditions such as hemorrhoids, infections, or irritable bowel syndrome.[1][2][3]
Rectal bleeding is one of the most common warning signs. Blood may appear bright red or cause the stool to look dark maroon or black and tarry. Some people may notice blood mixed with their stool or on toilet paper. While rectal bleeding is often caused by hemorrhoids, it should never be ignored and always deserves medical evaluation.[1][3][9]
Changes in bowel habits are another important symptom to watch for. This can include diarrhea, constipation, or more frequent bowel movements than usual. Some people notice that their bowel movement pattern changes in a way that persists over time. Others may feel that their bowel doesn’t empty completely even after going to the bathroom.[1][3][5]
The appearance of stools may change as well. Stools might become narrower than usual, sometimes described as thin as a pencil or stringy in appearance. This happens when a tumor narrows the opening through which stool passes.[1][2][9]
Other symptoms can include abdominal discomfort or pain, which may manifest as cramps, bloating, or a feeling of fullness. Some people experience unexplained weight loss, feeling tired or weak, or a general sense of not feeling well. A lump in the rectum may sometimes be felt during a medical examination. In more advanced cases, the cancer may cause a bowel obstruction, leading to severe symptoms that require immediate medical attention.[1][2][3][5]
Prevention Strategies and Screening Recommendations
The good news about rectal cancer is that it is often preventable through screening and lifestyle modifications. Most rectal cancers start as polyps, and these polyps can be discovered and removed during a colonoscopy before they have a chance to become cancerous. Because polyps typically take 10 to 15 years to transform into cancer, regular screening provides an excellent opportunity to prevent the disease entirely.[2][8]
Current guidelines recommend that all adults begin colorectal cancer screening at age 45. For people with higher risk factors—such as a family history of colorectal cancer, inflammatory bowel disease, or inherited genetic syndromes—screening may need to start earlier and occur more frequently. Colonoscopy is considered the gold standard for screening because it allows doctors to both detect and remove polyps during the same procedure.[3][5][8]
Beyond screening, several lifestyle changes can help reduce the risk of developing rectal cancer. Maintaining a healthy diet that includes plenty of fiber and limits red and processed meats may decrease risk. Evidence suggests that a high-fiber, low-fat diet may be protective. Staying physically active and maintaining a healthy weight are also important prevention strategies.[8]
Avoiding tobacco in all forms is crucial, as smoking has been linked to higher rates of rectal cancer death. Limiting alcohol consumption to no more than two drinks per day can also help reduce risk. While these lifestyle modifications cannot guarantee prevention, they represent actionable steps that individuals can take to lower their chances of developing the disease.[3][10]
How Rectal Cancer Changes Normal Body Function
To understand how rectal cancer affects the body, it helps to know how the digestive system normally works. The rectum is part of the body’s digestive system, which takes in nutrients from food and helps pass waste material out of the body. The digestive system consists of the esophagus, stomach, small intestine, and large intestine. The large intestine includes both the colon and the rectum.[3][5][10]
The colon, also called the large bowel, makes up the main part of the large intestine and is approximately five feet long. The rectum and anal canal together form the last six to eight inches of the large intestine. The rectum’s job is to store stool until it can be eliminated from the body through the anus. The anal canal ends at the anus, which is the opening through which waste leaves the body.[3][5][8][10]
Rectal cancer disrupts these normal functions in several ways. As a tumor grows on the inner lining of the rectum, it can gradually narrow the passage through which stool travels. This narrowing explains why people with rectal cancer may experience thin stools or feel that their bowel doesn’t empty completely. As the tumor continues to grow, it may eventually create a partial or complete blockage of the intestine.[1][2]
The tumor can also cause bleeding because it is made of abnormal cells that are more fragile than normal tissue and bleed easily. This bleeding may be visible in the stool or may occur internally, leading to anemia over time. Some people experience changes in bowel habits because the tumor interferes with the normal muscle contractions that move stool through the intestine.[1][2]
The rectum is located in a tight space within the pelvis, barely separated from other organs and structures including the bladder, reproductive organs, and major blood vessels. This anatomical reality means that as rectal cancer grows, it can potentially affect nearby organs and structures. The bony constraints of the pelvis also make surgical access to the rectum more challenging compared to the colon, which is one reason why rectal cancer requires specialized treatment approaches.[1][17]
Rectal cancer can spread beyond the rectum itself through several pathways. Cancer cells may invade through the layers of the rectal wall into nearby tissues. They can also travel through the lymphatic system to lymph nodes, or enter the bloodstream and spread to distant organs such as the liver or lungs. Understanding these potential patterns of spread is important for determining the stage of cancer and planning appropriate treatment.[4][17]