COLORECTAL CANCER

Types of Colorectal Cancer

Colorectal cancer is usually categorized based on where it starts and its cellular characteristics:

1. Adenocarcinoma:

   • The most common type, accounting for about 95% of colorectal cancers.
   • Arises from the mucus-producing glandular cells that line the colon and rectum.
   • Subtypes include: Mucinous adenocarcinoma and signet ring cell carcinoma, both of which tend to be more aggressive.

2. Carcinoid Tumors:

   • Arise from the hormone-producing cells in the intestine.
   • Tend to grow slowly and are often found incidentally.

3. Gastrointestinal Stromal Tumors (GIST):

   • A rare type of tumor that starts in the interstitial cells of Cajal in the digestive tract.
   • Can be benign or malignant.

4. Lymphomas:

   • A cancer that starts in the lymphatic system, which can sometimes begin in the colon or rectum.

5. Sarcomas:

   • Rare cancers that start in the blood vessels, muscle layers, or connective tissues of the colon and rectum.

Risk Factors

• Age: Most colorectal cancers occur in people over the age of 50, though it can occur at any age.
• Family History: A history of colorectal cancer or polyps in close relatives increases risk.
• Inherited Syndromes: Conditions like Lynch syndrome (hereditary nonpolyposis colorectal cancer, HNPCC) and familial adenomatous polyposis (FAP) significantly increase the risk.
• Personal History of Polyps or Cancer: Previous colorectal cancer or adenomatous polyps raise the risk of developing colorectal cancer.
• Inflammatory Bowel Disease: Chronic inflammatory conditions like ulcerative colitis or Crohn’s disease increase risk.
• Diet: Diets high in red and processed meats and low in fiber, fruits, and vegetables are linked to a higher risk.
• Obesity: Being overweight or obese increases the risk of colorectal cancer.
• Sedentary Lifestyle: Lack of physical activity is associated with an increased risk.
• Smoking and Alcohol: Long-term smoking and excessive alcohol use are risk factors.
• Type 2 Diabetes: People with type 2 diabetes have an increased risk of colorectal cancer.

Symptoms

Colorectal cancer may not cause symptoms in its early stages, but as it progresses, symptoms may include:

• Changes in Bowel Habits: Persistent diarrhea, constipation, or changes in stool consistency (e.g., narrower stools).
• Rectal Bleeding: Bright red or dark blood in the stool.
• Abdominal Discomfort: Persistent cramps, gas, or pain.
• Feeling of Incomplete Evacuation: A feeling that the bowel doesn’t empty completely.
• Weakness and Fatigue: Often due to anemia caused by chronic blood loss.
• Unexplained Weight Loss: Losing weight without trying can be a sign of cancer.
• Iron-Deficiency Anemia: Especially in men and postmenopausal women, can be an indication of bleeding in the colon.

Diagnosis

Diagnosing colorectal cancer typically involves several steps:

• Physical Examination and Medical History: The doctor will check for any abdominal masses or signs of anemia and ask about symptoms and risk factors.
• Colonoscopy: A procedure where a long, flexible tube with a camera (colonoscope) is inserted through the rectum to examine the entire colon. Polyps or suspicious areas can be biopsied.
• Sigmoidoscopy: Similar to a colonoscopy but only examines the rectum and lower part of the colon.
• CT Colonography (Virtual Colonoscopy): A non-invasive imaging test that uses CT scans to produce images of the colon and rectum.
• Fecal Occult Blood Test (FOBT) or Fecal Immunochemical Test (FIT): Tests that detect hidden blood in the stool, which can be an early sign of cancer.
• Stool DNA Test: A test that looks for certain DNA mutations in stool samples that are associated with colorectal cancer.
• Biopsy: Tissue samples taken during a colonoscopy are examined under a microscope to confirm the presence of cancer.
• Blood Tests: Including tests for anemia and tumor markers like CEA (carcinoembryonic antigen).

Staging

Once diagnosed, colorectal cancer is staged based on the extent of the disease:

• Stage 0 (Carcinoma in Situ): Cancer is only in the innermost lining of the colon or rectum.
• Stage I: Cancer has grown into the muscle layer of the colon or rectum but has not spread outside the colon or rectum.
• Stage II: Cancer has grown through the muscle layer to the outermost layers but has not spread to nearby lymph nodes.
• Stage III: Cancer has spread to nearby lymph nodes but not to other parts of the body.
• Stage IV: Cancer has spread to other parts of the body, such as the liver, lungs, or distant lymph nodes.

Treatment

Treatment for colorectal cancer depends on the stage, location, and overall health of the patient:

• Surgery:

  • Polypectomy and Local Excision: Removal of polyps or small, early-stage tumors during a colonoscopy.
  • Colectomy: Removal of part or all of the colon (partial colectomy) along with nearby lymph nodes.
  • Rectal Surgery: For rectal cancer, procedures like low anterior resection or abdominoperineal resection may be performed.

• Radiation Therapy:

  • Often used before surgery to shrink tumors, especially in rectal cancer, or after surgery to eliminate remaining cancer cells.

• Chemotherapy:

  • May be used before surgery (neoadjuvant) to shrink the tumor, after surgery (adjuvant) to reduce the risk of recurrence, or to treat advanced-stage cancer.

• Targeted Therapy:

  • Drugs that target specific molecules involved in cancer growth, such as VEGF inhibitors (e.g., bevacizumab) or EGFR inhibitors (e.g., cetuximab).

• Immunotherapy:

  • For certain types of advanced colorectal cancer, particularly those with high microsatellite instability (MSI-H) or mismatch repair deficiency (dMMR).

• Palliative Care:

  • Focuses on relieving symptoms and improving quality of life in advanced cancer cases.

Prognosis

The prognosis for colorectal cancer varies depending on the stage at diagnosis. Early detection greatly improves outcomes. The five-year survival rate for localized colorectal cancer (cancer that has not spread beyond the colon or rectum) is around 90%. However, survival rates decrease significantly if the cancer has spread to nearby lymph nodes or distant organs. For metastatic colorectal cancer (stage IV), the five-year survival rate is about 14%.

Prevention and Early Detection

• Screening: Regular screening, such as colonoscopy, starting at age 45 (or earlier for those with a family history or other risk factors), is key to early detection and prevention.
• Healthy Diet: A diet rich in fruits, vegetables, whole grains, and low in red and processed meats may reduce risk.
• Exercise: Regular physical activity is associated with a lower risk of colorectal cancer.
• Maintain a Healthy Weight: Avoiding obesity helps reduce the risk.
• Limit Alcohol and Quit Smoking: Both smoking and excessive alcohol use are linked to an increased risk of colorectal cancer.
• Aspirin: In some cases, low-dose aspirin may reduce the risk of colorectal cancer, particularly in people at high risk, but this should be discussed with a doctor.
• Genetic Counseling and Testing: For individuals with a strong family history of colorectal cancer or known genetic syndromes .