Bowel cancer

Bowel cancer, also referred to as colorectal cancer, is a malignant growth that arises in the colon or rectum, which are parts of the large intestine. It is one of the most common cancers worldwide and a major cause of cancer-related mortality. Early detection, prevention through screening, and advancements in treatment have significantly improved survival outcomes.

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Anatomy and Pathophysiology

The colon and rectum form the last part of the digestive tract. The colon absorbs water and salts, while the rectum stores waste before elimination. Bowel cancer usually develops from adenomatous polyps, which are abnormal tissue growths that can transform into cancer over years. The progression typically follows the adenoma-carcinoma sequence, where genetic mutations in tumor suppressor genes (e.g., APC, TP53) and oncogenes (e.g., KRAS) drive abnormal cell proliferation and malignancy.

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Risk Factors

Several factors increase the risk of bowel cancer:

• Age: Most cases occur in individuals over 50.

• Family history: Genetic syndromes such as Lynch syndrome (hereditary non-polyposis colorectal cancer) and familial adenomatous polyposis significantly increase risk.

• Lifestyle factors: Diets high in red and processed meats, low fiber intake, smoking, excessive alcohol consumption, and sedentary lifestyle contribute.

• Medical conditions: Inflammatory bowel disease (ulcerative colitis, Crohn’s disease) raises long-term risk.

• Obesity and diabetes: Both have been linked to higher incidence.

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Signs and Symptoms

Bowel cancer symptoms can vary depending on the location and stage:

• Persistent change in bowel habits (diarrhea, constipation, or alternating pattern)

• Blood in stool (hematochezia or melena)

• Abdominal pain, cramping, or bloating

• Unexplained weight loss

• Fatigue or anemia due to chronic blood loss

• Sensation of incomplete bowel emptying

In early stages, bowel cancer may be asymptomatic, highlighting the importance of screening.

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Diagnosis

Diagnosis involves a combination of clinical assessment, imaging, and laboratory investigations:

• Colonoscopy: Gold standard for detecting and removing polyps, with biopsy for histological confirmation.

• Fecal occult blood test (FOBT) or fecal immunochemical test (FIT): Screening tools to detect hidden blood in stool.

• CT colonography (virtual colonoscopy): Non-invasive imaging to visualize colon and rectum.

• Blood tests: Carcinoembryonic antigen (CEA) may be elevated but is mainly used to monitor recurrence.

• Imaging (CT/MRI scans): Determines extent of local invasion and distant metastasis (commonly to liver and lungs).

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Staging

Bowel cancer is staged according to the TNM system (Tumor, Nodes, Metastasis) and broadly classified into four stages:

• Stage I: Cancer confined to the inner lining of the colon or rectum.

• Stage II: Tumor has grown into or through the wall but has not spread to lymph nodes.

• Stage III: Spread to regional lymph nodes but not distant organs.

• Stage IV: Metastasis to distant organs such as liver or lungs.

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Treatment

Treatment depends on stage, location, and overall patient health. A multidisciplinary approach combining surgery, chemotherapy, radiotherapy, and targeted therapy is common.

1. Surgery

• Primary treatment for localized cancer.

• Types include partial colectomy, low anterior resection, or abdominoperineal resection.

• Laparoscopic and robotic surgeries are increasingly used.

• In advanced cases, surgery may relieve obstruction or bleeding.

2. Chemotherapy

Used for advanced disease or as adjuvant therapy after surgery to reduce recurrence risk.

• Common regimens:

  • 5-Fluorouracil (5-FU): 400–500 mg/m² IV bolus, often combined with leucovorin (20 mg/m²).

  • Capecitabine: 1,250 mg/m² orally twice daily for 14 days in a 21-day cycle.

  • Oxaliplatin: 85 mg/m² IV infusion every 2 weeks (often with 5-FU and leucovorin in the FOLFOX regimen).

  • Irinotecan: 180 mg/m² IV every 2 weeks (used in FOLFIRI regimen with 5-FU and leucovorin).

3. Radiotherapy

• Mainly for rectal cancer to shrink tumors preoperatively or to reduce recurrence risk postoperatively.

4. Targeted Therapies

• Bevacizumab (anti-VEGF monoclonal antibody): 5–10 mg/kg IV every 2 weeks, inhibits angiogenesis.

• Cetuximab and Panitumumab (EGFR inhibitors): Used in patients with wild-type KRAS/NRAS tumors. Cetuximab 400 mg/m² IV loading dose, followed by 250 mg/m² weekly.

• Regorafenib: 160 mg orally once daily for 21 days of a 28-day cycle, used in refractory metastatic cases.

5. Immunotherapy

• Pembrolizumab (anti-PD-1): 200 mg IV every 3 weeks, effective in tumors with microsatellite instability-high (MSI-H) or mismatch repair deficiency (dMMR).

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Prevention

• Screening: Colonoscopy every 10 years or FIT annually for individuals over 50 or earlier for high-risk groups.

• Lifestyle modification: High-fiber diet, reduced intake of processed meat, regular exercise, maintaining healthy weight, limiting alcohol, and quitting smoking.

• Aspirin prophylaxis: Low-dose aspirin has been associated with reduced risk, particularly in high-risk individuals, but must be weighed against bleeding risk.

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Prognosis

Survival rates depend on stage:

• Stage I: Over 90% 5-year survival.

• Stage II: Around 70–80%.

• Stage III: Approximately 50–60%.

• Stage IV: 10–15%, though improving with new therapies.

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Complications

• Bowel obstruction

• Perforation and peritonitis

• Chronic anemia

• Liver or lung metastasis

• Treatment-related toxicities (neuropathy from oxaliplatin, diarrhea from irinotecan, mucositis from 5-FU)

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Supportive Care

• Pain management: Analgesics and palliative care for advanced disease.

• Nutritional support: Address weight loss and malnutrition.

• Psychological support: Counseling and support groups for patients and families.

• Survivorship programs: Monitoring for recurrence and secondary cancers.