Colorectal cancer develops in the large intestine, which consists of the colon and the rectum. This cancer often originates from small, noncancerous growths called polyps on the inner wall of these organs. Over several years, some polyps can transform into cancerous tumors. The colon is the main part of the large intestine, while the rectum is the final section connecting to the anus. Because cancers in these locations share many features, they are often grouped.
Risk Factors and Prevention
A person’s risk for colorectal cancer is influenced by factors that cannot be changed. Age is a primary risk factor, with most cases occurring in individuals over 45. A personal or family history of colorectal cancer or polyps also increases risk, especially if a close relative developed the cancer at a young age.
Certain inherited genetic conditions elevate the risk. Familial adenomatous polyposis (FAP) causes numerous polyps to grow in the colon. Lynch syndrome, or HNPCC, is an inherited disorder that increases the risk for many cancers, including colorectal. A long-standing history of inflammatory bowel disease (IBD), like Crohn’s disease or ulcerative colitis, also increases risk due to chronic inflammation.
Lifestyle and environmental factors also play a role. Managing these factors can lower the risk of developing the disease. Key lifestyle-related risks include:
- Diets high in red and processed meats and low in fiber
- Lack of regular physical activity and obesity
- Smoking, which can increase the likelihood of developing polyps
- Heavy alcohol consumption
Preventive measures involve addressing these risks, such as adopting a diet rich in fruits and vegetables, exercising regularly, maintaining a healthy weight, quitting smoking, and reducing alcohol intake.
Symptoms and Signs
When symptoms of colorectal cancer appear, they can vary based on the tumor’s size and location. A common indicator is a persistent change in bowel habits, such as diarrhea, constipation, or a change in stool consistency that lasts for more than a few days.
Common signs and symptoms include:
- Rectal bleeding or blood in the stool, which may be bright red or make stool look dark
- Persistent abdominal discomfort, such as cramps, gas, or pain
- A feeling that the bowel does not empty completely
- Unexplained weight loss
- Weakness or fatigue, sometimes caused by anemia from chronic blood loss
- Nausea or vomiting, though this is less common
These symptoms are not exclusive to colorectal cancer and can be caused by other conditions like hemorrhoids or irritable bowel syndrome (IBS). The presence of these signs is not a definitive diagnosis. However, if any symptoms are persistent, a healthcare professional should be consulted for an evaluation.
Screening and Diagnosis
Screening aims to find colorectal cancer in people without symptoms, either by detecting it early or by removing polyps before they become cancerous. For individuals at average risk, screening is recommended to begin at age 45. Those with increased risk factors may be advised to start screening earlier.
Screening tests are categorized as either stool-based or visual exams. Stool-based tests are non-invasive, can be done at home, and include the fecal immunochemical test (FIT), guaiac-based fecal occult blood test (gFOBT), and stool DNA tests. These check for hidden blood or abnormal DNA in the stool.
Visual exams look directly at the colon and rectum. A colonoscopy is a primary method that uses a flexible tube with a camera to view the entire colon, allowing a doctor to remove polyps during the procedure. Other options include flexible sigmoidoscopy, which examines the lower colon, and CT colonography, which uses X-rays.
If a screening test is abnormal or a person has symptoms, a diagnostic workup is needed. This involves a colonoscopy to perform a biopsy, where a small tissue sample is taken from a suspicious area. Examining this tissue under a microscope is the definitive way to diagnose colorectal cancer.
After a diagnosis is confirmed, further tests gather more information. Blood tests can check for anemia and measure tumor markers like carcinoembryonic antigen (CEA). Imaging tests, such as a CT scan of the chest, abdomen, and pelvis, are used to see if the cancer has spread.
Staging of Colorectal Cancer
After diagnosis, the cancer’s stage is determined. Staging describes the tumor’s size and whether it has spread. This classification is used to plan the most effective treatment and provide an outlook on the disease.
The most common staging system is the TNM system. “T” (tumor) describes how far the tumor has grown into the colon or rectum wall. “N” (nodes) indicates if the cancer has spread to nearby lymph nodes. “M” (metastasis) refers to whether the cancer has spread to distant parts of the body, like the liver or lungs.
The TNM information is combined to assign a stage from 0 to IV. In Stage 0 (carcinoma in situ), abnormal cells are only in the innermost lining of the colon or rectum. In Stage I, the cancer has grown into deeper layers of the wall but has not spread outside of it.
In Stage II, the cancer has grown through the wall of the colon or rectum but has not spread to lymph nodes. Stage III is defined by the cancer spreading to one or more nearby lymph nodes, but not to distant sites.
Stage IV is the most advanced stage, meaning the cancer has metastasized. It has spread from the colon or rectum to distant organs. The most common sites of metastasis are the liver and lungs, but it can also spread to the bones or brain.
Treatment Approaches
Treatment for colorectal cancer depends on the cancer’s stage, its location, and the patient’s overall health. Plans are often developed by a team of specialists and may involve one or more approaches.
Surgery is the most common treatment, especially for earlier stages. The goal is to remove the tumor completely. For very early cancers, this may be done via polypectomy during a colonoscopy. For larger tumors, a colectomy removes the cancerous part of the colon and nearby lymph nodes. In some cases, an ostomy is created to allow waste to exit the body.
Chemotherapy uses drugs to kill cancer cells. It may be given after surgery (adjuvant chemotherapy) to eliminate remaining cells and reduce the risk of recurrence. For advanced cancers, chemotherapy can be the main treatment to shrink tumors and control the disease. The drugs are given intravenously or orally and travel through the bloodstream.
Radiation therapy uses high-energy rays to destroy cancer cells and is more common for rectal cancer than colon cancer. It may be used before surgery to shrink a tumor or after surgery to target remaining cancer cells. Radiation is often combined with chemotherapy to increase its effectiveness.
More advanced treatments are also available. Targeted therapy uses drugs that focus on specific molecules involved in cancer cell growth, blocking signals or cutting off the tumor’s blood supply. Immunotherapy helps the body’s immune system recognize and attack cancer cells. These are often used for advanced cancer with specific genetic characteristics.