Colorectal cancer is a type of cancer that originates in the colon or rectum. The colon and rectum are components of the gastrointestinal system, which plays a role in digestion.
Because colorectal cancer and rectal cancer share many common characteristics, they are often referred to interchangeably. Cancerous growths in the colon or rectum can potentially spread to other parts of the body.
Excluding skin cancers, colorectal cancer ranks as the third most common cancer in both men and women. The American Cancer Society estimated that around 142,570 cases of this type of cancer were expected in 2010. The mortality rates for this cancer have been decreasing due to early detection and removal of polyps.
Types of Colorectal Cancer:
More than 95 percent of colorectal cancer cases are of the type known as Adenocarcinoma. This is the type of cancer focused on in this article. Other rare types of cancer can be found in the colon and rectum.
Adenocarcinoma is a type of cancer that begins in the inner layer of the internal organs. "Adeno" refers to the gland. These growths start in cells with gland-like or secretory properties and are found in various organs, such as the lungs or breasts. In the colon, early detection of small growths (polyps) known as adenomatous polyps can continue to grow and potentially develop into cancerous growths. The majority of colorectal cancers are Adenocarcinomas.
Gastrointestinal stromal tumors (GISTs) are growths that originate in the muscle tissues of the digestive system. They are rare in the colon, and while they may be benign at first, many can become cancerous. When this happens, they are called sarcomas. Surgery is usually performed if the growth has not spread.
Lymphoma is a cancer that typically begins in the lymph nodes, part of the immune system. However, it can also start in the colon or rectum.
Carcinoids are growths that start in specialized cells responsible for producing hormones in the intestines. They often cause symptoms and can be treated with surgery.
Common Symptoms:
Individuals experiencing any of the following symptoms should consult their doctor, especially if they are over 50 years old or have a personal or family history of the disease:
- Changes in bowel habits, such as diarrhea, constipation, or prolonged bowel obstruction
- Rectal bleeding or blood in the stool
- Abdominal cramping or pain
- Loss of appetite
- Nausea or vomiting
- Weakness and fatigue
- Yellow discoloration of the skin and eyes (jaundice)
Symptoms of colorectal cancer can mimic other conditions, such as inflammation, infections, or inflammatory bowel diseases. Sometimes, colorectal cancer can be asymptomatic. Always consult with your doctor to get an accurate diagnosis.
Risk Factors:
Several factors increase the risk of developing colorectal cancer, including:
- Age: Most cases occur in people over the age of 50, but it can happen at any age.
- Race: African-Americans have the highest risk.
- Diet: This cancer is often associated with a diet high in red and processed meats.
- Polyps: Adenomatous growths in the colon or rectum are common in individuals over 50 and can lead to colorectal cancer.
- Personal history: People with a history of polyps are at increased risk of developing the disease.
- Family history: Individuals with a strong family history of colorectal cancer or polyps in close family members (especially before age 60) are at higher risk.
- Inflammatory bowel diseases, such as ulcerative colitis or Crohn's disease.
- Inherited syndromes, such as familial adenomatous polyposis (FAP) or hereditary nonpolyposis colorectal cancer (HNPCC).
- Overweight or obese.
- Sedentary lifestyle.
- Heavy alcohol consumption.
- Type 2 diabetes.
- Smoking.
Causes of Colorectal Cancer:
The exact cause is not known, but the factors listed above are the most likely contributors to the disease. A small percentage of colorectal cancers are caused by inherited gene mutations. Individuals with a strong family history of colorectal cancer should consider genetic testing, and it is recommended that anyone going through such testing consult with a qualified physician or genetic counselor to understand the implications of the results.
Prevention:
Although the exact cause of colorectal cancer is unknown, many cases can be prevented by taking the following actions:
- Diet, Weight, and Physical Activity: It's essential to reduce modifiable risk factors, such as diet, body weight, and physical activity. Eating more fruits, vegetables, and whole grains while reducing fat, low-fiber foods can be helpful. Regular physical activity can also reduce the risk.
- NSAIDs and Hormone Therapy: Low-dose nonsteroidal anti-inflammatory drugs (NSAIDs) and alternative hormone therapy for women during menopause may reduce the risk. However, these medications also come with risks, so it's essential to discuss this with your healthcare provider.
- Early Detection: The most critical factor in prevention is early detection through regular screenings at appropriate ages. Early detection can identify polyps in the colon that can be removed before they have the chance to become cancerous. While it's not possible to prevent all cases of colorectal cancer, early detection is the best way to improve the likelihood of successful treatment and reduce mortality rates.
Screening Methods:
Early detection of colorectal cancer for individuals with no symptoms or risk factors may involve the following methods:
- Fecal occult blood test (FOBT) annually
- Flexible sigmoidoscopy (FSIG) every five years
- Air-contrast barium enema every five years
- Colonoscopy every ten years
- Virtual colonoscopy (CT colonography) every five years
- Stool DNA test (sDNA)
Individuals with risk factors for colorectal cancer, such as strong family history, should start early screening at a younger age and have more frequent screenings.
Guidelines for Early Detection of Colorectal Cancer:
The American Cancer Society provides the following guidelines for early detection:
- Starting at age 50, both men and women should follow these guidelines:
- Annual fecal occult blood test (FOBT)
- Flexible sigmoidoscopy (FSIG) every five years
- Air-contrast barium enema every five years
- Colonoscopy every ten years
- Virtual colonoscopy (CT colonography) every five years
- Stool DNA test (sDNA)
- Individuals with a strong family history of colorectal cancer or polyps in close family members, especially before age 60, should start early screening at a younger age and/or have more frequent screenings.
- Families with hereditary colorectal cancer syndromes or other risk factors should undergo genetic counseling and start screening earlier.
Diagnosis of colorectal cancer:
If a person has symptoms that may be caused by colorectal cancer, the doctor will request a complete medical history and perform a physical examination. The doctor will also order specific tests to look for signs of cancer. Most of these tests are similar to those used for early detection of colorectal cancer in individuals without symptoms.
• Digital rectal examination: The doctor will insert a lubricated, gloved finger into the rectum to feel for any abnormalities or abnormalities. This examination can detect cancers in the rectum, but not in the rest of the colon.
• Fecal occult blood test: This test involves smearing a very small amount of stool on a special card, which is then examined in the clinic or sent to the laboratory.
• Flexible sigmoidoscopy: This diagnostic procedure allows the doctor to examine the inner part of the lower colon and is useful for identifying the causes of rectal bleeding, abdominal pain, constipation, growths, and inflammation. A short, flexible tube called a sigmoidoscope is inserted into the rectum. The sigmoidoscope inflates the colon with air and captures images of its inner lining.
• Colonoscopy: This procedure enables the doctor to view the entire colon and is often helpful in detecting growths, inflammatory tissues, polyps, and bleeding. It involves using a long, flexible tube called a colonoscope, which is inserted through the rectum into the colon. The colonoscope allows the doctor to see the inner lining of the colon, take tissue samples for biopsy, and, in some cases, perform treatments when abnormalities are found.
• Barium enema: This procedure involves filling the colon with a liquid called barium, which helps outline the colon on X-rays. The barium is injected into the colon through the rectum, and X-ray imaging of the abdomen reveals abnormalities, blockages, and other issues.
• Biopsy: During colonoscopy or surgeries, tissue samples are taken to determine if cancer or other abnormal cells are present.
• Complete blood count (CBC): This test is used to check for anemia, which may result from bleeding in the colon.
• Imaging tests: Imaging tests such as CT scans, ultrasound, or MRI can be used to locate tumors or other issues. These tests may be performed even if cancer has already been diagnosed to determine the cancer's stage.
Staging:
Once colorectal cancer is diagnosed, further tests are conducted to determine the tumor's size and whether it has spread to other parts of the body. This process is called staging and is an important step in planning the treatment. The American Cancer Institute defines the following stages:
Stage 0 (Carcinoma in situ): Cancer is found only in the innermost lining of the colon.
Stage I: Cancer has grown beyond the innermost lining of the colon into the second and third layers of the colon wall. It may have also spread outside the colon's outermost layer.
Stage II: Cancer has spread more deeply into or through the wall of the colon or to nearby tissues but has not involved nearby lymph nodes.
Stage III: Cancer has spread to nearby lymph nodes but has not affected other organs in the body.
Stage IV: Cancer has spread to other parts of the body, such as the lungs.
Treatment:
The specific treatment for colorectal cancer will be determined by the attending physician based on factors such as age, overall health, medical history, extent of the disease, and response to specific medications, treatments, or preferences.
Treatment may include:
• Surgery: Often, the initial treatment is a procedure called colon resection, in which the cancerous growth is removed along with the adjacent colon tissue on both sides of the growth and nearby lymph nodes.
• Radiation therapy involves using high-energy radiation to kill cancer cells and shrink tumors. Radiation therapy can be delivered externally or internally.
• External beam radiation: Treatment that delivers high and precise doses of radiation directly to the cancer cells. The computer controls the radiation delivery in the clinic. Radiation is used to kill cancer cells and shrink tumors. Special shields may be used to protect tissues surrounding the treatment area. External beam radiation typically lasts a few minutes and can cause discomfort.
• Internal radiation (brachytherapy): Internal radiation involves placing a radioactive material close to the cancer, either by inserting it into the blood, placing it inside the rectum, or implanting it directly into the tumor. Some radioactive implants are called "seeds" or "pellets." Brachytherapy allows a higher dose of radiation to be delivered in a shorter amount of time than external beam radiation. Internal radiation is temporary, and the radioactive material loses its radiation within a short period.
• Chemotherapy: Chemotherapy uses anti-cancer drugs to treat cancer cells. In most cases, chemotherapy works by disrupting the cancer cell's ability to grow or reproduce. Different groups of drugs work in different ways to fight cancer cells. An oncologist will recommend a treatment plan for each individual. Studies have shown that chemotherapy after surgery increases the survival rate of patients with certain stages of colon cancer. Chemotherapy can also help alleviate symptoms of advanced cancer.
Newer drugs that target specific treatments may be used alone or in combination with traditional chemotherapy to enhance effectiveness. For example, some newer drugs target proteins that are more prevalent in cancer cells than in normal cells. These drugs have different (and often rarer) side effects than conventional chemotherapy.