Colon Cancer
Basics
- Colon and rectal cancers (CRC) differ clinically but often grouped.
- 3rd leading cause of cancer deaths in US men and women.
- 2023 US new cases: ~106,970 colon, 46,050 rectal.
- Lifetime risk ~4.3% men, 3.9% women.
Epidemiology
- Incidence higher in men by ~33%.
- African Americans have highest incidence and mortality.
- Younger patients tend to present with advanced disease.
Etiology & Pathophysiology
- Progression over 10-15 years.
- High-risk polyps: multiple, villous/dysplastic, large (>1 cm).
- Genetic syndromes:
- Familial adenomatous polyposis (FAP): APC gene mutation.
- Lynch syndrome (HNPCC): mismatch repair genes (hMLH1, hMSH2, hMSH6, hPMS2, EPCAM).
- Peutz-Jeghers syndrome: STK11 mutation, mucocutaneous pigmentation.
- MUTYH-associated polyposis (MAP): base excision repair gene defects.
- Sporadic CRC: mutations in KRAS, PIK3CA, APC, TP53, BRCA1/2, BRAF.
Risk Factors
- Age ≥50 years (87% of new cases).
- Personal/family history of polyps or CRC.
- Inflammatory bowel disease (IBD), especially pancolitis in ulcerative colitis.
- Lifestyle: smoking, obesity, sedentary, high fat/low fiber diet, red/processed meats, alcohol.
- Radiation to abdomen/pelvis.
- Race/ethnicity disparities.
Prevention & Screening
- Lifestyle: high fiber diet, exercise.
- USPSTF: screening from age 45 (Grade B for 45-49, A for 50-75).
- Screening methods:
- Colonoscopy every 10 years.
- Flexible sigmoidoscopy (every 5-10 years) with FIT yearly.
- Stool-based tests: FIT annual, high-sensitivity gFOBT annual, stool DNA-FIT every 1-3 years.
- CT colonography every 5 years.
- Positive stool tests require colonoscopy.
- Family history or genetic syndromes require earlier/more frequent screening.
Diagnosis
History
- Microcytic iron-deficiency anemia (IDA) in men or postmenopausal women is CRC until proven otherwise.
- Symptoms: abdominal pain, bowel habit change, rectal bleeding, fatigue, weight loss.
Physical Exam
- Anemia signs.
- Weight loss.
- Palpable abdominal mass (late).
- Hepatomegaly, ascites, lymphadenopathy if metastasis.
Differential Diagnosis
- Adenocarcinomas (>95%).
- Carcinoid tumors, lymphomas, GIST, Kaposi sarcoma (HIV).
Diagnostic Tests
- Colonoscopy: diagnostic and therapeutic.
- CEA tumor marker: low sensitivity/specificity, useful for prognosis and monitoring.
- Imaging: contrast CT chest/abdomen/pelvis for metastases.
- PET scan for metastatic detection.
- SEER staging:
- Localized: no spread outside colon/rectum.
- Regional: spread to nearby structures.
- Distant: metastases to liver, lungs, distant nodes.
Treatment
- Surgery primary for localized disease with lymphadenectomy.
- Multivisceral resection for locally advanced.
- Resection of isolated metastases in liver/lungs can be considered.
- Adjuvant chemotherapy improves survival in stage III.
- Common regimens: FOLFOX, FOLFIRI, CAPEOX.
- Targeted/immunotherapy options: bevacizumab, ramucirumab, pembrolizumab, cetuximab, nivolumab, regorafenib.
Follow-Up
- Stage I/II: Colonoscopy at 1 year; if normal, then every 3 to 5 years.
- Stage III or node-positive: CEA and H&P every 3-6 months for 2 years, then every 6 months up to 5 years; annual CT chest/abdomen/pelvis for 5 years.
- Colonoscopy at 1 year post-op, then every 3-5 years if normal.
Patient Education
- CDC colorectal cancer screening information: https://www.cdc.gov/cancer/colorectal/basic_info/screening/tests.htm
Prognosis
- Overall 5-year survival ~65%.
- Localized: ~91%, regional: ~73%, distant: ~16%.
Complications
- Chemotherapy: alopecia, nausea, diarrhea, bruising, fatigue, infection risk.
- Radiation: skin irritation, rectal symptoms, bladder irritation, sexual dysfunction.
Clinical Pearls: