Colorectal cancer

Pathophysiology

Colorectal cancer probably arises from colorectal polyps. Adenomatous polyps convert to cancers at a rate of about 1% per year.

Treatment

Colorectal cancer treatment information from the National Cancer Institute's Physician Data Query

Medications

Aspirin

Aspirin may reduce mortality among patients whose tumor overexpress the enzyme cyclooxygenase 2 according to a cohort study. Cyclooxygenase 2 is expressed by most colorectal cancers and is associated with reduced survival.

Cetuximab

Cetuximab, an I_gG1 chimeric monoclonal antibody against epidermal growth factor receptor, may help according to a randomized controlled trial.

Prognosis

5-Year Relative Survival Rates By Year Dx By Cancer Site All Ages, All Races, Both Sexes 1975-2000.

Staging information

Colorectal cancer staging information from the National Cancer Institute's Physician Data Query

Prognosis of colonic cancer

Stage	Five-year survival rate (%)
Stage I (T1-2N0)	93
Stage IIA (T3N0)	85
Stage IIB (T4N0)	72
Stage IIIA (T1-2 N1)	83
Stage IIIB (T3-4 N1)	64
Stage IIIC (N2)	44
Stage IV	8

Screening

In the United States, both underuse and overuse of screening occur.

Practice guidelines

A clinical practice guideline by the US Preventive Services Task Force has addressed colorectal cancer:

• "recommends screening for colorectal cancer using fecal occult blood testing, sigmoidoscopy, or colonoscopy in adults, beginning at age 50 years and continuing until age 75 years."

• "recommends against routine screening for colorectal cancer in adults 76 to 85 years of age. There may be considerations that support colorectal cancer screening in an individual patient."

• "recommends against screening for colorectal cancer in adults older than age 85 years"

• "the evidence is insufficient to assess the benefits and harms of computed tomographic colonography and fecal DNA testing (a subsequent study found that DNA was more sensitive but less specific)"

A clinical practice guideline jointly written by the American Cancer Society and other groups recommends one of:

• Flexible sigmoidoscopy every 5 years
• Barium enema every 5 years
• Virtual colonography (a noninvasive test based on computed tomography) every 5 years
• Colonoscopy every 10 years

When polyps are found, a clinical practice guideline jointly written by the American Cancer Society and other groups states:

• High risk polyps are 1) 3 or more synchronous adenomas, 2) adenomas ≥1 cm in diameter, or 3) villous histology or high-grade dysplasia.
• High risk polyps should have follow-up colonoscopy in 3 years
• Low risk polyps should have repeat colonoscopy in 5 to 10 years
• If no adenomas are found, follow-up evaluation should be at 10 years

Evidence

A meta-analysis has reviewed studies of fecal testing and colonic imaging.

A validation of guidelines found:

• High risk adenomas - 9% of an advanced adenoma at 4 years of follow-up.
• Low risk adenomas - 5% of an advanced adenoma at 4 years of follow-up.

Visualization

Selected studies of the benefit of visualization from colorectal cancer screening

Procedure	Study	Benefit	Number needed to screen (assuming control rate of 1%)
Fecal occult blood annually	Minnesota Colon Cancer Control Study Randomized controlled trial 46,551 patients for 13 years	Colorectal cancer death: Relative risk ratio 0.67 Relative risk reduction 33%	305
Double-contrast barium enema	Ontario Cancer Registry Cohort study 13,849 patients who had a DCBE 36 months prior to the diagnosis of CRC	Colorectal cancer incidence: False negative rate (1-Sensitivity) 22% Sensitivity 78%	142
Sigmoidoscopy	Kaiser Permanente Case-control study 261 case patients and 868 control patients for 10 years	Colorectal cancer death: Odds ratio 0.41	170
	Telemark Polyp Study I Cohort study 400 case patients and 399 controls for 7 to 11 years	Colorectal cancer incidence: Relative risk ratio 0.2 Relative risk reduction 80%	125
Colonoscopy	National Polyp Study Cohort study 1418 patients for 5.8 years	Colorectal cancer incidence: Relative risk ratio 0.1 Relative risk reduction 90%	111
	Ontario Cancer Registry Case-control study 10,292 case patients and 51,460 controls for 7.8 years	Colorectal cancer death: Odds ratio 0.69	325

Visualization may be less effective in the right colon.

Capsule endoscopy

Capsule endoscopy is less accurate than optical endoscopy.

Prevention

Aspirin chemoprophylaxis

A clinical practice guideline by the U.S. Preventive Services Task Force (USPSTF) recommended against taking aspirin (grade D recommendation). The Task Force acknowledged that aspirin may reduce the incidence of colorectal cancer, but "concluded that harms outweigh the benefits of aspirin and NSAID use for the prevention of colorectal cancer". Long-term doses over 81 mg per day may increase bleeding events.

Subsequent meta-analyses conclude:

• "300 mg or more of aspirin a day for about 5 years is effective in primary prevention of colorectal cancer in randomised controlled trials, with a latency of about 10 years".
• "Aspirin is effective for the prevention of colorectal adenomas in individuals with a history of these lesions." The number needed to treat was about 33.

Calcium

A meta-analysis by the Cochrane Collaboration of randomized controlled trials published through 2002 concluded "Although the evidence from two RCTs suggests that calcium supplementation might contribute to a moderate degree to the prevention of colorectal adenomatous polyps, this does not constitute sufficient evidence to recommend the general use of calcium supplements to prevent colorectal cancer.". Subsequently, one randomized controlled trial by the Women's Health Initiative (WHI) reported negative results. A second randomized controlled trial reported reduction in all cancers, but had insufficient colorectal cancers for analysis.