An 18-year-old man presents to his primary care provider before leaving for college. He has no complaints. His past medical history is significant for asthma, acne vulgaris, and infectious mononucleosis at age 16. His home medications include doxycycline and albuterol as needed. His family history is significant for colon cancer in his father at age 50, his paternal grandfather at age 55, and an uncle at age 45. His father underwent testing for mutations in the APC gene, which were negative. There is no family history of dental abnormalities or other malignancy. The patient denies any recent weight loss, abdominal pain, hematochezia, melena, or other changes in the appearance of his stools. This patient should be screened for colorectal cancer (CRC) under which of the following protocols?

Colonoscopy every 5 years beginning at age 40

Colonoscopy every 10 years beginning at age 50

Colonoscopy every 1-2 years beginning at age 25

Fecal occult blood testing annually beginning at age 40

A 50-year-old Caucasian man presents for a routine checkup. He does not have any current complaint. He is healthy and takes no medications. He has smoked 10–15 cigarettes per day for the past 10 years. His family history is negative for gastrointestinal disorders. Which of the following screening tests is recommended for this patient according to the United States Preventive Services Task Force (USPSTF)?

Colonoscopy for colorectal cancer

Abdominal ultrasonography for abdominal aortic aneurysm

Carcinoembryonic antigen for colorectal cancer

Low-dose computerized tomography for lung cancer

Prostate-specific antigen for prostate cancer

A 46-year-old woman presents to her primary care physician for her annual examination. At her prior exam one year earlier, she had a Pap smear which was within normal limits. Which of the following health screenings is recommended for this patient?

Blood glucose and/or HbA1c screening

Blood pressure at least once every 3 years

A 19-year-old woman presents to the physician for a routine health maintenance examination. She has a past medical history of gastroesophageal reflux disease. She recently moved to a new city to begin her undergraduate studies. Her father was diagnosed with colon cancer at age 46. Her father's brother died because of small bowel cancer. Her paternal grandfather died because of stomach cancer. She takes a vitamin supplement. Current medications include esomeprazole and a multivitamin. She smoked 1 pack of cigarettes daily for 3 years but quit 2 years ago. She drinks 1–2 alcoholic beverages on the weekends. She appears healthy. Vital signs are within normal limits. Physical examination shows no abnormalities. Colonoscopy is unremarkable. Germline testing via DNA sequencing in this patient shows mutations in DNA repair genes MLH1 and MSH2. Which of the following will this patient most likely require at some point in her life?

Annual colonoscopy beginning at 20–25 years of age

Surgical removal of a desmoid tumor

Prophylactic proctocolectomy with ileoanal anastomosis

Measurement of carcinoembryonic antigen and CA 19-9 yearly

A 65-year-old man presents to his primary care physician for a yearly checkup. He states he feels he has been in good health other than minor fatigue, which he attributes to aging. The patient has a past medical history of hypertension and is currently taking chlorthalidone. He drinks 1 glass of red wine every night. He has lost 5 pounds since his last appointment 4 months ago. His temperature is 99.2°F (37.3°C), blood pressure is 147/98 mmHg, pulse is 80/min, respirations are 14/min, and oxygen saturation is 99% on room air. Physical exam reveals an obese man in no acute distress. Laboratory values are ordered as seen below. Hemoglobin: 9 g/dL Hematocrit: 27% Mean corpuscular volume: 72 µm^3 Leukocyte count: 6,500/mm^3 with normal differential Platelet count: 193,000/mm^3 Serum: Na+: 139 mEq/L Cl-: 101 mEq/L K+: 4.3 mEq/L HCO3-: 25 mEq/L BUN: 20 mg/dL Glucose: 99 mg/dL Creatinine: 1.1 mg/dL Ca2+: 9.0 mg/dL AST: 32 U/L ALT: 20 U/L 25-OH vitamin D: 15 ng/mL Which of the following is the best next step in management?

Counseling for alcohol cessation

Exercise regimen and weight loss

A 46-year-old man presents with increasing fatigue and weakness for the past 3 months. He works as a lawyer and is handling a complicated criminal case which is very stressful, and he attributes his fatigue to his work. He lost 2.3 kg (5.0 lb) during this time despite no change in diet or activity level. His past history is significant for chronic constipation and infrequent episodes of bloody stools. Family history is significant for his father and paternal uncle who died of colon cancer and who were both known to possess a genetic mutation for the disease. He has never had a colonoscopy or had any genetic testing performed. Physical examination is significant for conjunctival pallor. A colonoscopy is performed and reveals few adenomatous polyps. Histopathologic examination shows high-grade dysplasia and genetic testing reveals the same mutation as his father and uncle. The patient is concerned about his 20-year-old son. Which of the following is the most appropriate advice regarding this patient's son?

A genetic test followed by colonoscopy for the son should be ordered.

The son doesn't need to be tested now.

An immediate colonoscopy should be ordered for the son.

Screening can be started by 50 years of age as the son’s risk is similar to the general population.

The son should undergo a prophylactic colonic resection.

Colorectal cancer screening for USMLE Step 3: High-Yield Internal Medicine Lessons

CRC Basics - Why We Screen

Goal: Detect & remove precancerous polyps (adenomas) to prevent progression to adenocarcinoma.
Adenoma-Carcinoma Sequence: Slow, multi-step progression (mutations in APC, KRAS, p53) over ~10-15 years, creating a wide window for intervention.
Epidemiology: 2nd leading cause of US cancer death. Most cases are sporadic.
Key Risk Factors: Age >45, 1st-degree relative with CRC, IBD (UC > Crohn's), obesity.

⭐ Most CRCs arise from adenomatous polyps. Right-sided lesions often present with iron deficiency anemia; left-sided lesions cause changes in stool caliber.

Colonoscopy views: normal, polyps, and familial polyposis

Screening Modalities - The Toolbox

A comparison of available CRC screening tests:

Test	Frequency	Pros	Cons
Stool-Based
FIT	Annually	No prep, non-invasive	Lower sensitivity for polyps
gFOBT	Annually	Inexpensive	Low sensitivity/specificity, dietary restrictions
sDNA-FIT	Every 3 yrs	↑ sensitivity for cancer vs. FIT	Expensive, ↑ false positives
Visual
Colonoscopy	Every 10 yrs	Gold standard; diagnostic & therapeutic	Invasive, full prep, sedation risk
CT Colonography	Every 5 yrs	Less invasive, no sedation	Prep needed, radiation, can't biopsy
Flex Sigmoidoscopy	Every 5 yrs	Less prep	Views only distal 1/3 of colon

⭐ Exam Favorite: Unlike the guaiac-based FOBT (gFOBT), the Fecal Immunochemical Test (FIT) is specific for human globin and does not require dietary or medication restrictions (e.g., avoiding red meat, iron supplements, or vitamin C), leading to better patient adherence and fewer false positives.

Screening Algorithms - The Playbook

Routine screening for average-risk individuals begins at age 45 and continues until age 75. The decision to screen between ages 76-85 is individualized, weighing life expectancy and comorbidities. Screening is generally discontinued after age 85.

Tier 1 (Prevent & Detect):
- Colonoscopy every 10 years.
Tier 2 (Detection Only):
- Fecal Immunochemical Test (FIT) annually.
- Stool DNA-FIT (e.g., Cologuard) every 1-3 years.
- CT Colonography every 5 years.
- Flexible Sigmoidoscopy every 5 years.

⭐ Any positive non-colonoscopy screening test (FIT, Sigmoid, Cologuard) must be followed by a diagnostic colonoscopy to be considered a complete screening.

High-Risk Groups - The Exceptions

Family Hx (CRC/Advanced Adenoma):
- FDR <60y: Scope at 40y or 10y before diagnosis, q5y.
- FDR ≥60y: Scope at 40y, q10y.
Inflammatory Bowel Disease (UC/Crohn's):
- Scope 8 years post-pancolitis dx, q1-2y with biopsies.
Genetic Syndromes:
- FAP: Sigmoidoscopy @ 10-12y.
- Lynch (HNPCC): Colonoscopy @ 20-25y, q1-2y.

⭐ In IBD, surveillance requires extensive random biopsies (e.g., 4-quadrant every 10 cm) as dysplasia can be flat and invisible.

Sigmoidoscopy and colonic polyps

High‑Yield Points - ⚡ Biggest Takeaways

Average-risk colorectal cancer screening now begins at age 45.

Colonoscopy every 10 years is the preferred screening strategy; annual FIT is the best non-invasive test.

For a first-degree relative with CRC diagnosed at <60 years, start screening at age 40 or 10 years before the relative's diagnosis.

Lynch syndrome and FAP are high-risk conditions requiring much earlier and more frequent surveillance.

Screening is generally discontinued after age 75.

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