Our large intestines—made up of the cecum, colon and rectum—are the last stop in our digestive system. Sometimes, a small growth, called a polyp, can form on the inner wall of the colon or rectum. Although many polyps are benign (not cancerous), some become cancerous when a change in the DNA causes abnormal cells to grow.

Colorectal cancer is the third most common cancer in the United States, with more than 150,000 new cases occurring each year. In fact, according to a 2024 report from the American Cancer Society, colorectal cancer has moved up from being the fourth leading cause of cancer death in both men and women under age 50 two decades ago to first in men and second in women. (Breast cancer is the leading cause of death in women under 50.)

Though some cases are inherited, for many patients the exact cause can be hard to pinpoint. Treatment depends on how advanced the cancer has become but often includes some type of surgery to remove the tumor.

“With advances in surgery, radiation, and chemotherapy many patients can be cured,” says co-director of the Colorectal Cancer Program at Smilow Cancer Hospital Michael Cecchini, MD.

Though incidence is rising in young people, most cases of colorectal cancer affect older adults. It has been linked to inflammatory bowel disease (disorders involving chronic inflammation of your digestive tract like Crohn’s disease and ulcerative colitis). It’s also been associated with certain lifestyle factors, such as cigarette smoking, heavy alcohol consumption, a lack of exercise and a high-fat and low-fiber diet.

About 20 percent of colorectal cancer patients have a family history of the disease, possibly due to one of the following inherited conditions:

• Familial adenomatous polyposis (FAP), which causes hundreds or even thousands of polyps to form in the colon.
• MUTYH-associated polyposis (MAP) syndrome, which is a more recently discovered disorder that resembles FAP.
• Gardner syndrome, which results in the development of numerous polyps along with other abnormal lesions.
• Lynch syndrome, or hereditary nonpolyposis colorectal cancer, which often affects people at a younger age and can lead to cancers in other parts of the body as well.

Symptoms depend on the location, type and stage of the cancer. The most common symptom of colorectal cancer is a change in bowel habits. Patients may also notice blood in the stool, as well as unexplained weight loss. Occult bleeding (bleeding that you can’t see) in the stool may also cause weakness and fatigue. 

But the truth is, because colorectal cancer grows slowly, symptoms may not appear for a long time. That’s why screening is so important for detecting cancer at an early stage.

Colonoscopy, one of the recommended screening tests for people age 45 or over, is also used to diagnose colorectal cancer in patients who are experiencing symptoms associated with the disease.   

During the procedure, a doctor uses a tool called a colonoscope, which has a tiny camera, to check for polyps or abnormal tissue in the large intestine. One benefit of having regular colonoscopies is that any potentially pre-cancerous or cancerous polyps are removed on the spot, to prevent the disease from even starting.

If a doctor finds a tumor during the procedure, a sample of the tumor is taken to be looked at under a microscope, and then the patient is referred to a surgeon for treatment. Meanwhile, lab tests can be done to confirm the diagnosis.

The American Joint Committee on Cancer has developed a staging system for colorectal cancer—ranging from stage 0 (least invasive) to stage IV (most invasive)—that doctors use to determine the best treatment plan.

Surgery is usually the first part of treatment. For early-stage cancers, the tumor and small portions of the bowel may be removed, allowing digestive function to remain intact. For more advanced disease, a colostomy (an opening in the colon) or ileostomy (an opening in the ileum, which is part of the small intestine) may be created as a temporary or permanent pathway for waste.

Patients with advanced cancer also typically receive some combination of chemotherapy and radiation therapy. Stage IV disease means that the cancer has spread to other parts of the body, so the treatment strategy will need to be tailored to the patient’s individual needs.

“At Yale, we have a world class multidisciplinary care team with expertise in the diagnosis and treatment of colorectal cancer,” says Dr. Cecchini. “We have a weekly dedicated colorectal cancer tumor board involving colorectal experts in pathology, radiation, nuclear medicine, surgery, radiation oncology, and medical oncology. In the clinic, we also have specialized nurses, social workers, geneticists, and nutritionists that are critical members of our care team. We ensure that all patients seen at Yale get the specialized care they deserve, and our robust team will provide exceptional care ranging from the most up-to-date surgical techniques to innovative clinical trials.”