Colorectal cancer is one of the most common cancers diagnosed in the United States, but it’s actually two separate cancers—colon cancer and rectal cancer. Both the colon and the rectum are part of the large intestine, but which cancer you have depends on where the cancer starts.
“The term colorectal cancer is often useful because many things about these two cancers are the same,” says UNC Health medical oncologist Michael Iglesia, MD, PhD. “One thing that can be very different, though, is the treatment.”
Of the two cancers, colon cancer is more common. The American Cancer Society estimates that in 2026, there will be about 108,860 new cases of colon cancer and 49,990 new cases of rectal cancer. Some of that difference can be attributed to size: the colon is 5 to 6 feet long, and the rectum, which connects the colon and the anus, is only about 6 inches long.
One thing that these two cancers unfortunately share: they’re both on the rise in people under the age of 50.
“Among people who have early onset colorectal cancer, colon cancer is more common overall, but there’s a higher proportion of these young patients who have rectal cancer than in older patient groups,” Dr. Iglesia says.
Dr. Iglesia explains risk factors and symptoms to know, as well as what you can expect from treatment.
Rectal Cancer Risk Factors
The risk factors for both colon and rectal cancers are the same. Age is a key one; while these cancers are on the rise in young people, most cases still happen in people who are older than 50. Family history and other medical conditions also play a role.
“We know people with a first-degree relative who had colorectal cancer are at a higher risk themselves,” Dr. Iglesia says. “Certain genetic conditions, most notably Lynch syndrome, increase your risk. Inflammatory bowel disease, such as ulcerative colitis, increases your risk in the areas where the disease causes inflammation.”
If you are part of one of these high-risk groups, your doctor will help you determine when and how often you should start colorectal cancer screening. If you’re not part of a high-risk group and don’t have any concerning symptoms, you should get your first colonoscopy at age 45.
You can’t control your genetic risk for cancer, but many other risk factors can be addressed.
“You can decrease your risk for both colon and rectal cancer by increasing the amount of dietary fiber you consume and decreasing the amount of ultraprocessed foods, red meat and alcohol,” Dr. Iglesia says. “Maintain a healthy body weight and get regular physical activity.”
The increase of ultraprocessed foods in the American diet may be one of the factors driving the rise of colorectal cancer in young people, but Dr. Iglesia says that no hypothesis has been definitively proven, and many people who eat healthy, well-balanced diets still get colorectal cancer.
“Another hypothesis is something is causing a change to the gut microbiome,” he says. “Bacteria are a normal part of our gut flora, but there might be an increased risk if you have a certain strain. It’s not yet clear what’s causing that change.”
Rectal Cancer Symptoms and Diagnosis
Like colon cancer, rectal cancer doesn’t always have symptoms in its earliest stages, but there are important red flags to note.
“Always pay attention to any blood in your stool or any bleeding from your rectum,” Dr. Iglesia says. “If you have unexplained weight loss or anemia or any change in normal bowel movements, talk to your doctor.”
Rectal cancer has a unique symptom.
“With a tumor in the rectum, you might feel like you can’t empty your bowels fully,” Dr. Iglesia says. “One of the jobs of the rectal wall is to sense when there’s stool in the rectum and send a signal to the brain to use the bathroom. The cancer, and then the treatment, can irritate that rectal wall muscle so that you might feel that you need to use the bathroom more frequently.”
Here’s some good news: a colonoscopy can be used to diagnose both colon cancer and rectal cancer. It can also prevent both diseases, because your doctor can remove polyps from the colon or rectal wall before they become cancerous. That’s a major advantage over at-home stool kits, which are effective at detecting both types of cancer but have a low detection rate of polyps.
“A colonoscopy is the best test for screening of any cancer of the colon or rectum,” Dr. Iglesia says. “One reason we emphasize regular colonoscopies is because when rectal cancer is found early, it has a very high chance of cure with treatment.”
Rectal Cancer Treatment
Here’s where colon cancer and rectal cancer are most different: If you’re diagnosed with colon cancer, your typical first step will be surgical removal of the tumor from your colon, which is then typically followed by chemotherapy.
“With rectal cancer, we try to minimize surgical invention in the rectum, because the rectal wall is thinner and there’s a higher risk of complications with surgery,” Dr. Iglesia says; complications can include bowel incontinence and sexual dysfunction. “We start with chemotherapy and radiation.”
The precise combination and length of chemotherapy and radiation will vary for everyone; your doctor will consider the size and location of your tumor, if there’s been any spread of the disease and your overall health.
“It’s a lot more individualized and tailored to the patient compared to colon cancer right now,” Dr. Iglesia says. “It’s also a rapidly evolving field with many potential new treatments. There are clinical trials looking at the best way to combine chemotherapy and radiation for the patient, as well as several new drugs and targeted therapies for specific gene mutations.”
Chemotherapy and radiation is extremely effective in early disease that hasn’t spread beyond the rectum. For some patients, this treatment cures rectal cancer.
“We do careful surveillance and follow the patients for five years after a curative treatment, because there is a risk of recurrence,” Dr. Iglesia says.
If you have been diagnosed with rectal cancer, Dr. Iglesia encourages you to connect with a support group.
“It’s important to get plugged in with people who share this experience,” he says. “Hearing what other people have gone through alleviates anxiety and can help you understand all the new information that comes with a diagnosis.”
If you’re concerned about your risk for colorectal cancer, talk to your doctor or find one near you.