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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
Key points
- Average-risk adults: begin CRC screening at age 45 and continue through 75
- Age 76-85: individualized; stop after 85
- Colonoscopy every 10 years or annual FIT are common screening options
- Right-sided cancer often presents with iron deficiency anemia; left-sided cancer with obstruction or stool caliber change
- Family history or hereditary syndromes require earlier and more frequent screening
Overview
Colorectal cancer usually develops through adenoma-carcinoma or serrated pathways over years. Screening prevents cancer by detecting/removing premalignant polyps and reduces mortality by finding early-stage disease.
Epidemiology
CRC is a leading cause of cancer death in the United States. Incidence has declined in older adults due to screening but has risen in younger adults, prompting average-risk screening from age 45.
Clinical Features
Symptoms
Occult bleeding or iron deficiency anemia
Change in bowel habits or stool caliber
Hematochezia, abdominal pain, weight loss
Large bowel obstruction
Persistent rectal bleeding with anemia or weight loss
Signs
Often normal early
Pallor from anemia
Abdominal mass or hepatomegaly in advanced disease
Rectal mass on DRE if distal lesion
Investigations
First-line
Screening testColonoscopy, annual FIT, stool DNA-FIT, CT colonography, or sigmoidoscopy depending on interval/preference
CBC and iron studiesEvaluate anemia
Colonoscopy with biopsyDiagnostic test for symptoms or abnormal screening
Second-line
CEABaseline for prognosis/surveillance after diagnosis; not screening
CT chest/abdomen/pelvisStaging after diagnosis
Specialist
Genetic testingYoung onset, multiple cancers, or strong family history
MMR/MSI testingPerformed on CRC tumor tissue
1
Average-risk screening
- Start at age 45
- Colonoscopy every 10 years or annual FIT are common choices
- Abnormal stool test requires colonoscopy
- Individualize age 76-85; stop after 85
2
Increased risk
- First-degree relative: start earlier, often age 40 or 10 years before youngest diagnosis
- IBD colitis surveillance usually begins 8 years after onset
- Lynch syndrome requires frequent early colonoscopy
3
Treatment
- Localized colon cancer: surgical resection with lymph node evaluation
- Adjuvant chemotherapy for stage III and selected high-risk stage II
- Rectal cancer often needs MRI staging and multimodal therapy
Complications
- Obstruction: More common left-sided.
- Iron deficiency anemia: Classic right-sided presentation.
- Metastasis: Liver via portal circulation.
- Perforation: Emergency presentation.
USMLE Step 2 CK Exam Tips
- 1Average-risk screening starts at 45
- 2Positive FIT/stool DNA means colonoscopy
- 3Right colon cancer = iron deficiency anemia
- 4Left colon cancer = obstruction/change in caliber
- 5CEA is surveillance/prognosis, not screening
- 6Lynch: colon + endometrial cancer, MSI/MMR defects
- 7Do not dismiss rectal bleeding as hemorrhoids with alarm features
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