Definition:
Colorectal cancer (CRC) is a malignant epithelial tumor arising from the mucosa of the colon or rectum. It is typically an adenocarcinoma, originating from glandular epithelial cells.
Classification:
By Location:
- Proximal type (right-sided): coecum, colon ascendens, colon transversum
- Distal type (left-sided): colon descendens, sigma, rectum
By Morphology:
- Polypoid type – protruding mass
- Ulcerative type – ulcerated tumor with necrotic center
- Infiltrative type – circumferential growth causing stenosis
- Solitary type – single, localized tumor mass
Etiology / Risk Factors:
- Adenomatous polyps (especially villous)
- Chronic inflammatory bowel disease:
- Ulcerative colitis
- Crohn’s disease
- Low-fiber, high-fat diet
- Genetic syndromes: FAP, HNPCC (Lynch syndrome)
- Constipation (longer transit time → carcinogen exposure)
- Cholecystectomy (altered bile acid metabolism)
Pathogenesis:
- Progression follows the adenoma-carcinoma sequence:
- 1. Normal mucosa → adenomatous polyp → dysplasia → carcinoma
- 2. Mutations in APC, KRAS, and p53 genes are common.
- Microsatellite instability in cases of Lynch syndrome
Symptoms:
Proximal Colon Tumors:
- Vague abdominal discomfort or pain
- Iron-deficiency anemia (fatigue, pallor, tachycardia)
- Unexplained fever
- Weight loss, anorexia
- Sometimes abdominal mass or obstruction
Distal Colon / Rectal Tumors:
- Rectal bleeding (rectorrhagia): blood mixed with feces
- Change in bowel habits: constipation alternating with diarrhea
- Painful defecation, tenesmus
- Fatigue, weight loss (due to anemia and tumor burden)
- Severe perianal pain if plexus is involved
End-Stage Disease (Metastases):
- Liver metastases: hepatomegaly, jaundice, RUQ pain
- Peritoneal metastases: ascites
- Pulmonary metastases: cough, hemoptysis, dyspnea
- Rarely: renal failure, lung embolism, peritonitis from perforation