Colorectal cancer
Colorectal cancer is an adenocarcinoma that arises through the adenoma-carcinoma sequence and presents differently by location, with right-sided tumors causing occult bleeding and iron-deficiency anemia and left-sided tumors causing obstruction and hematochezia. Colonoscopy with biopsy confirms the diagnosis, TNM staging on CT chest/abdomen/pelvis with CEA guides treatment, and management ranges from surgical resection alone for localized disease to adjuvant FOLFOX for node-positive colon cancer, neoadjuvant chemoradiation for rectal cancer, and molecularly targeted systemic therapy for metastatic disease.
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What this article covers
- Overview
Definition: colorectal cancer is an adenocarcinoma arising from the colonic or rectal mucosa, usually through stepwise transformation of a benign adenomatous polyp into invasive carcinoma over 8 to 10 years.
- Epidemiology
Third most common cancer and the second leading cause of cancer death among men and women in the United States, with roughly 145,600 new cases annually.
- Risk factors
Age 50 years or older: the dominant nonmodifiable risk factor, though incidence under 50 is rising.
- Pathophysiology
Adenoma-carcinoma sequence: most cancers begin as an adenomatous polyp that accumulates sequential mutations over about 8 to 10 years before becoming invasive.
- Clinical features
Often asymptomatic, especially early-stage disease detected only by screening.
- Differential diagnosis
Diverticular bleeding or diverticulitis: painless hematochezia or left lower quadrant pain and fever without a discrete mass on colonoscopy (Diverticulosis).
- Diagnosis
Colonoscopy with biopsy is the confirmatory test: direct visualization with histologic biopsy showing adenocarcinoma establishes the diagnosis; complete the colonoscopy to the cecum when possible to exclude synchronous lesions.
- Management
Stage I (localized, no nodal involvement): surgical resection alone (segmental colectomy, or transanal excision for small superficial rectal tumors); no adjuvant treatment unless more extensive disease is found intraoperatively.
- Complications
Metastatic spread: most often to the liver via the portal circulation, and to the lung; defines stage IV disease and drives the sharp drop in survival.
- Prognosis
Stage is the dominant prognostic factor: 5-year disease-free survival is 90% to 95% for stage I, 70% to 85% for stage II, 25% to 70% for stage III, and 0% to 10% for stage IV.
- Prevention
Average-risk screening: colonoscopy every 10 years or annual FIT beginning at age 45 (USPSTF and American Cancer Society); the American College of Physicians endorses beginning at age 50.
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