Colorectal Cancer: Symptoms, Screening, Risk Factors and Treatment

What colorectal cancer is and why early detection matters

Colon and rectal cancers affect different parts of the large intestine, but clinicians often discuss them together as colorectal cancer because they share many features. Most begin as polyps, abnormal growths in the lining of the colon or rectum. Polyps aren’t cancer, though some can change over time. More than 90 percent of these cancers are adenocarcinomas, which develop from glandular cells lining the intestine.

Colorectal cancer is the fourth most common cancer among adults in the United States, excluding skin cancers, and ranks second among cancer deaths. Rates have fallen among people older than 50, while cases in people under 50 have risen. That pattern makes it useful to know both the warning signs and the screening options available to people who feel well.

Symptoms to discuss with a clinician

Colorectal cancer can cause changes that also occur with conditions such as hemorrhoids, so a symptom by itself doesn’t establish the cause. Persistent or unexplained changes deserve medical attention. Signs can include:

• A change in bowel habits, such as diarrhea, constipation or narrower stools, lasting more than a few days
• A continuing sense that a bowel movement is needed, even after having one
• Rectal bleeding, bright red blood or darker stools
• Abdominal pain or cramping
• Unexplained weight loss

Bleeding can also contribute to anemia, a low red blood cell count that may leave someone tired or weak. If a symptom is new, persistent or concerning, a clinician can review it alongside a person’s health and family history.

Who may have a higher risk

Risk reflects a mix of inherited biology and other factors. A small number of people develop colorectal cancer because of rare inherited gene changes, but most cases don’t have a single known cause. Factors associated with increased risk include excess weight, limited physical activity, a diet high in red or processed meat, smoking, moderate to heavy alcohol use and type 2 diabetes.

Other factors include age, being a man, a personal or family history of colorectal cancer or polyps, and inflammatory bowel disease such as Crohn’s disease or ulcerative colitis. Lynch syndrome is a rare inherited condition that can substantially raise the chance of colorectal cancer and other cancers. A family history involving multiple close relatives may be a reason to discuss inherited risk with a clinician. For people with Lynch syndrome, the source estimates a lifetime risk of colon cancer as high as 80 percent and of endometrial cancer as high as 60 percent.

Rates and outcomes also differ among racial and ethnic groups. Native American, Alaska Native and Black people in the United States have higher rates of new cases and deaths than other groups and may face obstacles to screening. Some evidence suggests Black people may be more likely to carry certain genetic changes linked to more aggressive tumors. These patterns don’t predict an individual’s outcome, but they underscore the value of discussing personal risk and access to screening with a healthcare professional.

Screening and diagnosis

Screening can find cancer before symptoms appear and can detect polyps that may be removed before they become cancerous. Finding cancer earlier can also make it more treatable. For people at average risk, screening is recommended from ages 45 through 75. People with higher risk may be advised to begin earlier. The appropriate test and interval depend on risk, prior results and the method used, so timing is best discussed with a clinician.

Available tests include stool tests that look for hidden blood or abnormal DNA or RNA. A fecal immunochemical test uses antibodies to detect blood; a guaiac-based test uses a chemical reaction to find it. A blood test may look for changes associated with cancer or precancerous growths, but it’s less sensitive than other screening methods and isn’t a preferred screening choice.

Colonoscopy uses a flexible camera to examine the colon. Clinicians can remove suspicious tissue during the procedure, and the tissue can then be examined under a microscope. Sigmoidoscopy looks at only the lower part of the colon and is used rarely. CT colonography, sometimes called virtual colonoscopy, uses X-rays to create images of the colon and rectum. It’s less invasive than colonoscopy but may be less thorough.

A positive screening test or symptoms generally call for follow-up. A clinician may review symptoms and health history, perform an examination and recommend colonoscopy. A digital rectal exam, in which a gloved finger is used to feel for lumps, may also be part of the assessment. A biopsy, or examination of a tissue sample, confirms whether cancer cells are present.

What staging tells the care team

After diagnosis, imaging and other tests help show how far the cancer has grown or spread. Clinicians may use CT, MRI or PET scans and, in some cases, a lymph node biopsy. They assess whether cancer is limited to the inner lining, has grown into the intestinal wall, has reached nearby lymph nodes or has spread to other organs. The resulting stage ranges from 0 to 4. In general, a lower stage means the disease is less advanced, though stage alone can’t describe every person’s outlook.

Treatment depends on the cancer’s features and extent

Care may include surgery, radiation, medicines or a combination. The choice depends on where the cancer is, how far it has spread and other details of the tumor and the person’s health. Surgery is often the first treatment for early colon cancer and is used for most rectal cancers. In some cases, doctors can remove diseased tissue during colonoscopy; in others, they remove part of the colon or rectum.

After a section is removed, the remaining ends may be reconnected. Sometimes a colostomy is needed: an opening in the abdomen lets stool pass into a collection bag. The source describes this as usually temporary. If cancer has spread to other organs, tumors there may be removed during the first operation or later.

Radiation uses energy to destroy cancer cells. It may be given before surgery to shrink a tumor or afterward to target remaining cells. It’s used more often for rectal than colon cancer, and may also be used when cancer has spread.

Medicines are often considered when cancer has spread, returned after earlier treatment, or when treatment around surgery may help shrink a tumor or address remaining cells. Chemotherapy drugs work throughout the body; examples include capecitabine, fluorouracil, irinotecan, oxaliplatin, and trifluridine with tipiracil.

Targeted medicines act on specific features of cancer cells. Tumor testing can help determine whether a target is present. Medicines listed for advanced colorectal cancer include adagrasib, bevacizumab, cetuximab, encorafenib, fruquintinib, panitumumab, ramucirumab, regorafenib, tucatinib and ziv-aflibercept. Encorafenib may also be paired with fluorouracil-based chemotherapy and cetuximab.

Immunotherapy helps the immune system recognize and attack cancer. Checkpoint inhibitors have helped a subset of people whose tumors have particular genetic changes. Options listed include atezolizumab, dostarlimab, ipilimumab, nivolumab and pembrolizumab. These medicines aren’t suitable for every tumor; treatment choices depend on test results and clinical assessment.

Complications, follow-up and support

A tumor can cause bleeding, blockage of the colon or, less commonly, a hole in the intestinal wall. Cancer can spread to other sites; the liver is the most common destination described, though the lungs and other areas of the abdomen can also be affected.

After treatment, bowel function may change. Diarrhea or fecal incontinence can be temporary or lasting, and a clinician can help address these problems. People with a colostomy can work with a trained therapist to learn care and adapt daily activities. Follow-up after colorectal cancer may include regular colonoscopies, blood tests for carcinoembryonic antigen (a protein that tumor cells can shed), and CT scans of the chest, abdomen and pelvis. The schedule depends on the person’s situation.

Support organizations can offer practical information and connection with others. The Colorectal Cancer Alliance’s BlueHQ hub links patients and caregivers with patient navigators and peers. Fight Colorectal Cancer offers resources such as a doctor finder, clinical trial search and financial assistance listings. The Colon Cancer Coalition’s Faces of Blue platform lets people share experiences and read survivor stories.

Risk reduction in perspective

There’s no guaranteed way to prevent colorectal cancer. Not smoking, staying physically active, maintaining a healthy weight, limiting alcohol and keeping red and processed meat to a minimum may help lower risk. Screening remains a key part of prevention because it can identify and remove some polyps. For personal symptoms, family history, screening timing or treatment questions, a doctor or pharmacist can help clarify what information applies to an individual.