The Function of the Colon and Complications Associated with Colorectal Cancer

The colon, also known as the large intestine, plays a crucial role in the digestive system. Its primary functions include the absorption of water and salts from the material that has not been digested as food, and the formation and excretion of feces. The colon also houses beneficial bacteria that aid in digestion and produce essential vitamins like vitamin K.

When colorectal cancer (CRC)—which includes cancers of the colon and rectum—develops, it significantly disrupts these vital processes. It may cause bleeding, absorption dysfunction, obstruction, or even perforation of the colon wall. Advanced cases may lead to bowel obstruction, metastatic spread (especially to the liver or lungs), cachexia (wasting syndrome), and systemic metabolic deterioration. The presence of cancer in the colon can also impair nutritional status, immune function, and overall quality of life.

Categories Associated with Primary and Secondary Colorectal Tumours

Colorectal cancer may be classified under two broad categories:

Primary Colorectal Cancer

This originates in the tissues of the colon or rectum. The most prevalent type is adenocarcinoma, which starts in the mucus-producing glands lining the colon or rectum. Other less common types include:

• Mucinous adenocarcinoma

• Signet-ring cell carcinoma

• Squamous cell carcinoma

• Gastrointestinal stromal tumors (GIST)

• Neuroendocrine tumors

Secondary (Metastatic) Colorectal Cancer

These are cancers that began in another part of the body (such as the breast, stomach, or pancreas) and have spread (metastasized) to the colon or rectum. Conversely, colorectal cancer often metastasizes to the liver, lungs, peritoneum, or bones.

Causes and Risk Factors

Several factors contribute to the development of colorectal cancer, often over many years. These include:

• Age: Risk increases significantly after age 50

• Genetics: Family history, Lynch syndrome, and Familial Adenomatous Polyposis (FAP)

• Diet: High intake of red or processed meats, low fiber intake

• Inflammatory bowel diseases: Crohn’s disease and ulcerative colitis

• Obesity and physical inactivity

• Smoking and heavy alcohol use

• Type 2 diabetes

• History of polyps or previous colorectal cancer

• Radiation therapy to the abdomen or pelvis

Signs and Symptoms of Colorectal Cancer

Colorectal cancer is often asymptomatic in early stages, making regular screening essential. As it progresses, symptoms may include:

• Persistent changes in bowel habits (constipation, diarrhea, or narrowing of stool)

• Blood in stool or rectal bleeding

• Abdominal pain, cramping, bloating, or discomfort

• Fatigue or generalized weakness

• Unexplained weight loss

• A feeling that the bowel does not empty completely

• Anemia-related symptoms due to chronic blood loss

• Nausea or vomiting in advanced cases

Diagnosis of Colorectal Cancer

Diagnosis involves a combination of clinical assessments and diagnostic tools:

• Medical History and Physical Examination

• Digital Rectal Exam (DRE)

• Fecal Tests:

  • Fecal Immunochemical Test (FIT)

  • Fecal Occult Blood Test (FOBT)

  • Stool DNA test (e.g., Cologuard)

• Endoscopic Evaluation:

  • Colonoscopy (gold standard)

  • Sigmoidoscopy

  • Biopsy (during colonoscopy)

• Imaging Studies:

  • CT colonography (virtual colonoscopy)

  • Abdominal/pelvic CT or MRI

  • PET scans for staging

• Laboratory Tests:

  • Complete Blood Count (CBC)

  • Liver Function Tests

  • CEA (Carcinoembryonic Antigen) levels – a tumor marker

• Staging:
  Cancer staging (Stage 0–IV) using the TNM system helps in treatment planning and prognosis evaluation.

Best Treatment for Colorectal Cancer

Treatment depends on the cancer’s location (colon or rectum), size, stage, and patient’s overall health.

A. Traditional Treatments

1. Surgical Procedures

• Polypectomy: For very early-stage cancers confined to polyps

• Partial Colectomy: Removing the section of the colon with cancer

• Total Colectomy: In cases with widespread disease

• Colostomy/Ileostomy: If reconnection isn’t possible

• Rectal Surgery: For cancers in the lower rectum, possibly requiring resection with anastomosis or permanent stoma

2. Radiation Therapy

• Commonly used for rectal cancer, either before surgery to shrink tumors or after surgery to kill remaining cells

• External beam radiation therapy is the standard method

3. Systemic Chemotherapy

• Used after surgery (adjuvant), before surgery (neoadjuvant), or for metastatic disease

• Common drugs include:

  • 5-FU (Fluorouracil)

  • Oxaliplatin

  • Capecitabine

  • Irinotecan

• Side effects: fatigue, diarrhea, low blood count, neuropathy

B. Advanced and Alternative Treatments for Colorectal Cancer

1. Minimally Invasive and Microinvasive Therapies

• Laparoscopic or Robotic Surgery: Less invasive surgeries with faster recovery

• Radiofrequency Ablation (RFA) and Microwave Ablation (MWA) for liver metastases

• Cryoablation for localized tumors

2. Targeted Therapy

• Monoclonal antibodies against specific molecules:

  • Bevacizumab (targets VEGF – blood vessel growth)

  • Cetuximab, Panitumumab (targets EGFR – cell growth)

• Fewer side effects than traditional chemotherapy

3. Immunotherapy

• Primarily used in MSI-H/dMMR tumors (Microsatellite Instability-High / Deficient Mismatch Repair)

• Drugs include:

  • Pembrolizumab (Keytruda)

  • Nivolumab + Ipilimumab

• Reprograms immune system to attack cancer without harming healthy cells

4. Brachytherapy and Radioembolization

• Used mainly for rectal or liver metastases

• Radioactive beads deliver localized radiation to tumor tissue while sparing normal tissue

5. Stem Cell and Future Therapies

• Experimental use of CAR-T Cell Therapy and stem-cell-mediated immune restoration is being studied for resistant forms of CRC

Prevention and Lifestyle Management

Preventing colorectal cancer involves reducing risk factors and early detection:

• Regular Screening: Begin at age 45, earlier if high risk

• Diet: High in fiber, fruits, vegetables; low in red/processed meats

• Exercise: At least 30 minutes of physical activity most days

• Avoid Alcohol and Smoking

• Maintain Healthy Weight

• Treat Chronic Diseases: Proper management of IBD and diabetes

• Prophylactic Surgery: In patients with hereditary cancer syndromes

• Aspirin Use: May reduce risk (under medical advice)

Prognosis and Survival Rates

Prognosis depends on the stage at diagnosis and response to treatment:

• Stage I: 90–95% 5-year survival

• Stage II: 70–85%

• Stage III: 50–70%

• Stage IV (metastatic): ~10–15%

Survival rates have improved with advanced screening, targeted therapies, and earlier interventions. Regular follow-up is crucial to detect recurrence or metastasis early.

Conclusion

Colorectal cancer, encompassing both colon and rectal malignancies, remains a significant cause of cancer morbidity and mortality globally. Understanding its risk factors, promoting early detection through regular screenings, and implementing comprehensive treatment strategies—ranging from surgery to advanced immunotherapies—can significantly enhance survival outcomes. Public awareness and proactive lifestyle choices are essential in reducing the burden of this preventable disease.