Colorectal Cancer: Symptoms, Types, and Screening Guidelines

Colorectal cancer remains a significant public health challenge, ranking as the second leading cause of cancer-related deaths in the United States when combined data for men and women are used. In 2025, it is estimated that 154,270 new cases will be diagnosed, resulting in approximately 52,900 deaths. However, early detection significantly alters the prognosis; the five-year survival rate for individuals diagnosed at an early stage (stage I-II) is about 91%.

Because the disease often begins as precancerous polyps—small, usually harmless growths in the colon or rectum—regular screening is critical. These polyps can be identified and removed before they transition into cancer. Due to rising rates of the disease in younger populations, the American Cancer Society and the US Preventive Services Task Force now recommend that adults at average risk begin regular screening at age 45.

Types and Stages of Colorectal Cancer

Colorectal cancer refers to malignancies that originate in the colon or the rectum. The most common form is adenocarcinoma, which begins in the cells lining the surface of the colon. Other less common types include carcinoid tumors, which start in hormone-producing cells; gastrointestinal (GI) stomal tumors, which begin in the nerve cells of the GI tract wall; and lymphomas, which are cancers of the immune system that can manifest in the colon or rectum.

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The disease is categorized into stages based on the extent of its spread:

• Stage 0: The cancer is located only in the innermost lining.
• Stage I: The cancer grows into the colon wall but has not spread to the lymph nodes.
• Stage II: The cancer extends through the colon wall, but lymph nodes remain unaffected.
• Stage III: The cancer has spread to nearby lymph nodes.
• Stage IV: The cancer has metastasized to distant organs, such as the lungs or liver.

Identifying Symptoms and Warning Signs

In its early stages, colorectal cancer may not produce any noticeable symptoms. When symptoms do appear, they often affect the digestive system. Common warning signs include a change in bowel habits—such as persistent constipation, diarrhea, or stool narrowing—that lasts more than a few days, as well as a feeling that a bowel movement is incomplete.

Bleeding is a primary indicator, appearing as bright red rectal bleeding or darker blood within the stool. Other symptoms include cramping, abdominal pain, unintended weight loss, and general weakness or fatigue.

The location of the tumor can influence the symptoms. Left-sided colon cancer, which accounts for the majority of cases, more frequently causes digestive changes and bloody stool. Right-sided colon cancer is less common and is more likely to lead to fatigue, weight loss, and anemia.

Continuous, slow blood loss into the digestive tract can lead to anemia, a condition characterized by a low red blood cell count. In some instances, blood tests that diagnose anemia serve as the initial step toward a colorectal cancer diagnosis.

Potential Complications

If left undiagnosed, colorectal cancer can lead to severe complications. A tumor may partially or completely block the colon, resulting in a bowel obstruction that causes nausea, bloating, and pain. In more dangerous cases, a bowel perforation—a tear in the colon wall—can occur, leading to infection in the abdominal cavity and requiring emergency surgery.

Tumors can also cause life-threatening hemorrhages or metastasis, where the cancer spreads to the lymph nodes, liver, or lungs, impairing the function of those organs.

Diagnosis can be delayed because symptoms often mimic more common conditions, such as irritable bowel syndrome or hemorrhoids. Younger adults may ignore symptoms under the assumption that the disease only affects the elderly. However, rates are climbing sharply in people under 50, and it is estimated that by 2030, approximately 15 percent of all colorectal cancer cases will be diagnosed in younger adults.

Screening Guidelines and Options

Screening is used to detect the disease in people who do not have symptoms. For those at average risk, the US Preventive Services Task Force recommends screening for adults age 45 to 75. For those aged 76 to 85, the decision to screen should be made on an individual basis considering health, preferences, and prior history. People over age 85 are generally advised to stop screening.

Individuals are considered average risk if they do not have a personal or family history of colorectal cancer or certain polyps, a history of radiation to the abdomen or pelvic area, or a personal history of inflammatory bowel disease (such as ulcerative colitis or Crohn’s disease). Those with genetic syndromes, such as Lynch syndrome or familial adenomatous polyposis (FAP), are at increased risk and should consult a doctor regarding earlier and more frequent testing.

Available screening options include:

• Stool-based tests: Highly sensitive fecal immunochemical tests (FIT) or guaiac-based fecal occult blood tests (gFOBT) performed every year, or multi-targeted stool DNA tests (MT-sDNA/FIT-DNA) every three years.
• Visual exams: A colonoscopy performed every 10 years, or CT colonography or sigmoidology every five years.

The Diagnostic Process

When a patient presents with symptoms or a positive screening result, doctors perform a medical exam and review the patient’s history, looking for risk factors such as obesity, low physical activity, smoking, and heavy alcohol use. A physical examination may include a digital rectal exam to feel for abnormalities.

The primary diagnostic tool is the colonoscopy, where a gastroenterologist uses a flexible tube with a camera to examine the interior of the rectum and colon. If suspicious growths are found, the physician can remove tissue for a biopsy to determine if cancer cells are present.