Colorectal Cancer
Cancer of the large intestine or rectum, typically growing from pre-cancerous polyps over many years.
Emergency Management: Malignant large bowel obstruction causing massive dilation. Requires emergent diverting colostomy or endoscopic stenting.
A malignant neoplasm arising from the mucosal epithelium of the colon or rectum. The vast majority are adenocarcinomas evolving through the adenoma-carcinoma sequence.
Detailed Overview
CRC is a major cause of cancer morbidity and mortality worldwide. It develops slowly, taking 10-15 years for a benign adenomatous polyp to undergo malignant transformation via acquired genetic mutations (APC, KRAS, TP53). Early stages are often asymptomatic, making screening colonoscopy starting at age 45 crucial. Right-sided lesions cause occult bleeding and anemia, while left-sided lesions cause obstruction and changes in bowel habits.
Epidemiology & Demographics
Third most common cancer and second leading cause of cancer death globally. Incidence is rising in adults under 50. Lifetime risk is roughly 4-5%.
Etiological Mechanism
Sporadic genetic mutations (80%), familial syndromes like Lynch syndrome or FAP (5-10%), or inflammatory bowel disease.
Primary Causes
Sequential accumulation of somatic mutations in the mucosal epithelium.
Chromosomal Instability Pathway (85%): Loss of the APC tumor suppressor gene leads to early adenoma. Subsequent mutation of the KRAS oncogene promotes late adenoma formation. Finally, loss of TP53 leads to frank adenocarcinoma. Microsatellite Instability Pathway (15%): Defective DNA mismatch repair genes (MLH1, MSH2) result in rapid accumulation of mutations, classic in Lynch Syndrome.
Diagnostic Criteria & Guidelines
Direct visualization via colonoscopy with biopsy confirming adenocarcinoma.
Surgical resection is the primary treatment (e.g., right hemicolectomy, LAR, or APR) with at least 12 regional lymph nodes removed. Neoadjuvant chemoradiation is standard for rectal cancers (Stage II/III) before surgery.
Second-Line & Adjunctive Therapy
Adjuvant chemotherapy (FOLFOX: 5-FU, Leucovorin, Oxaliplatin) for 3-6 months for Stage III (node-positive) colon cancer. Biologics (Bevacizumab targeting VEGF, or Cetuximab targeting EGFR if KRAS wild-type) for metastatic Stage IV disease.
Surgical & Procedural Management
Low Anterior Resection (LAR) for upper/mid rectal tumors. Abdominoperineal Resection (APR) with permanent colostomy for low rectal tumors invading the sphincter.
Patient Counseling & Advice
Ensure all first-degree relatives are informed, as they need early screening colonoscopy (10 years prior to the age of diagnosis of the patient).
Follow-Up & Monitoring Schedule
CEA testing every 3-6 months for 2 years. Colonoscopy at 1 year post-op, then 3 years, then every 5 years. Annual CT Chest/Abd/Pelvis for up to 5 years to monitor for hepatic/pulmonary mets.
Preventive Strategies
Screening via colonoscopy every 10 years starting at age 45 (or FIT test annually). Polypectomy removes the precursor lesion, directly preventing cancer.
Highly dependent on stage at diagnosis. Overall 5-year survival is 65%, but drops to 14% if metastatic.