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Screening for colorectal cancer: Strategies in patients at average risk

Last literature review version 17.3: September 2009  |  This topic last updated: July 17, 2009   (More)

INTRODUCTION — Colorectal cancer (CRC) is a common and lethal disease; removal of premalignant adenomas can prevent the cancer and removal of localized cancer may prevent CRC-related death. CRC is infrequent before age 40; the incidence rises progressively thereafter to 3.7/1000 per year by age 80 (graph 1). The lifetime incidence for patients at average risk is 5 percent [1], with 90 percent of cases occurring after age 50.

CRC is the second leading cause of cancer death, and accounts for approximately 9 percent of cancer deaths overall [2]. Approximately one in three people who develop CRC die of this disease. Incidence rates have been declining in the United States (US). The onset of the decline somewhat predates widespread screening and the extent to which the decline can be attributed to screening, or to change in behavioral risk factors, is unknown. (See "Colorectal cancer: Epidemiology, risk factors, and protective factors".)

Screening rates for CRC, although rising in the US over the past few years, are generally below national targets, despite evidence that screening reduces colon cancer mortality [3]. US data from 2006 indicate that 60.8 percent of adults >50 years old had received colorectal cancer screening [3,4]. Screening rates are higher in adults who are insured, better educated, non-Hispanic, or have a usual source of medical care [5].

This topic addresses the rationale and modalities recommended for CRC screening in patients who are at average risk for the disease. Screening recommendations for patients at increased risk, as well as surveillance for colorectal cancer in patients with colon polyps, are addressed separately. (See "Screening for colorectal cancer: Strategies in patients with possible increased risk due to family history" and "Screening and management strategies for patients and families with familial colon cancer syndromes" and "Approach to the patient with colonic polyps".)

PATHOGENESIS

Adenoma-carcinoma sequence — Most colorectal cancers arise from adenomatous polyps that progress from small to large (>1.0 cm) polyps, and then to dysplasia and cancer. Neoplastic changes likely result from both inherited and acquired genetic defects [6].

The progression from adenoma to carcinoma, when it occurs, apparently takes at least ten years on average [7], although polyps are ordinarily removed when found so this estimate is imprecise. Polyps and cancers are distributed approximately evenly throughout the colon and rectum, though tend to be more proximal in women, and with increasing age.

Some colon cancers arise from non-polypoid adenomas that are flat or depressed and account for 22 to 36 percent of identified adenomas [8-10]. Flat and depressed lesions are difficult to detect and are recognizable only by subtle distortion of the mucosal pattern and special stains [9]. Large flat adenomas may be more likely to contain dysplastic changes [9] or cancer [8] than polypoid ones of comparable size.

Most colorectal polyps are either adenomatous or hyperplastic. These cannot be distinguished reliably by gross appearance; biopsy is required for diagnosis (picture 1). Hyperplastic polyps usually do not progress to cancer. (See "Approach to the patient with colonic polyps".)

  • Two-thirds of polyps are adenomas. Adenomas are found in about 25 percent of colonoscopies performed in people age 50, and in 50 percent of people age 70 or younger (graph 2). Large adenomatous polyps (>1.0 cm) are more likely to progress to cancer than smaller ones, but are less common [11].
  • Hyperplastic polyps account for most of the remaining polyps and are typically small and distal. Although generally not premalignant, there are reports of cancers arising from hyperplastic polyps [12]. A rare syndrome, hyperplastic polyposis, is associated with a large number of hyperplastic polyps and an increased risk of CRC [13]. (See "Approach to the patient with colonic polyps".)

The risk of CRC increases with adenoma size, number, and histology (eg, villous adenomas greater risk than tubular adenomas) (picture 2) [14,15]. The finding of one adenomatous polyp suggests a propensity to form polyps and the patient should be evaluated for other lesions in the colon and rectum. The number and types of lesions found will determine the appropriate interval for subsequent surveillance colonoscopy.

Removal of adenomatous polyps prevents cancer. The National Polyp Study Work Group followed 1418 patients in whom colonoscopic examination led to the removal of one or more polyps [16]. During a mean follow-up of six years, the incidence of colon cancer was 88 to 90 percent lower than in patients reported in other studies who had polyps that were not removed, and 76 percent lower than in the general population.

RISK FACTORS — The risk of developing CRC is largely acquired, although genetic factors also play a role. The incidence of CRC varies about 15-fold across regions of the world, and people who move from low- to high-risk regions acquire higher rates during their lifetime [17].

In the United States, both incidence and mortality from CRC are higher in black patients compared with white patients [2]. This may relate to differences in screening rates, environmental factors, or tumor biology. In a study of patients who had screening colonoscopy, the risk of finding polyps (>9 mm) was greater in black patients compared to white patients (7.7 versus 6.2 percent), with the risk disproportionately higher in women [18]. For patients over 60 years, proximal lesions were more common in black patients than white patients.

Several dietary and behavioral risk factors have been suggested by observational studies (table 1) [19]. A meta-analysis of observational studies concluded that smokers, compared to never smokers, had an increased risk for CRC of approximately 20 percent (RR 1.18, 95% CI 1.11-1.25) [20]. Currently, risk factors other than age and family history are not taken into account in screening recommendations. (See "Colorectal cancer: Epidemiology, risk factors, and protective factors" and "Cancer prevention".)

Detection of increased risk — Before deciding how best to screen, and when to initiate screening, clinicians should determine the individual patient's level of risk. A decision tool to determine risk for CRC, applicable only to non-Hispanic whites, has been developed by the National Cancer Institute and incorporates data relevant to age, diet, exercise, medication use, and colonoscopy results as well as family history in first degree relatives [21,22]. However, current guidelines take into account only personal and family history of polyps and cancer when recommending a screening program.

A few questions will help determine if the patient may be at increased risk for colorectal cancer [23]:

  • Have you ever had colorectal cancer or an adenomatous polyp?
  • Have you had inflammatory bowel disease (ulcerative colitis or Crohn's disease)?
  • Have any family members had colorectal cancer or an adenomatous polyp?

     - If so, how many, were they first-degree relatives (parent, sibling, or child), and at what age was the cancer or polyp first diagnosed?

The patient is considered at average risk if all answers to the three initial questions are "no". Patients answering "yes" to any of these questions may be at increased risk and need to be evaluated further. (See "Screening for colorectal cancer: Strategies in patients with possible increased risk due to family history".)

We suggest asking these questions by age 20, and every five years thereafter, although there are no published guidelines specifying this age or frequency. Most high risk patients should begin CRC screening at an earlier age than those at average risk. (See "Screening for colorectal cancer: Strategies in patients with possible increased risk due to family history".)

Risk factors that affect screening recommendations

Strong genetic risk

  • Hereditary nonpolyposis colon cancer — Hereditary nonpolyposis colorectal cancer (HNPCC), a familial form of CRC caused by mutations in DNA mismatch repair genes, accounts for approximately 2 to 3 percent of colorectal cancer. HNPCC also increases risk for other cancers, including colorectal, endometrial, stomach, ovarian, pancreas, ureters and kidney, biliary tract, and brain (usually glioblastoma). (See "Clinical features and diagnosis of Lynch syndrome (hereditary nonpolyposis colorectal cancer)".)

The diagnosis should be considered in people with more than one family member with CRC or other HNPCC-related cancer occurring at a young age, commonly in the 30s and 40s.

Other significant risks

  • Prior colorectal cancer or polyps — A prior history of CRC increases the risk of another primary (metachronous) cancer. The magnitude of risk is not precisely known, although it has been reported to be about 1.5 to 3 times the risk in the general population [24,25]. A history of adenomatous colorectal polyps also increases the risk of CRC, especially if the polyps are multiple, large, or have villous architecture [26]. (See "Approach to the patient with colonic polyps".)

  • Inflammatory bowel disease — The association between colonic inflammatory bowel disease (ulcerative colitis or Crohn's disease) and increased risk of CRC is well documented for extensive (pancolitis) and longstanding disease. Cancers develop in areas of dysplasia, rather than from polyps. (See "Colorectal cancer surveillance in inflammatory bowel disease".)

  • Race — Black persons, compared to other racial and ethnic groups, have the highest incidence of CRC, and the CRC mortality rate is nearly double that for other minority groups [33]. While American College of Gastroenterology 2008 guidelines recommend initiating screening in African Americans beginning at age 45 years [34], other US national guidelines do not propose earlier screening based only on racial background [35,36].
  • Other risks — Gardner's syndrome (CRC with benign extracolonic tumors) and Turcot's syndrome (CRC with brain tumors) are less common inherited syndromes. These syndromes appear to result from expression of the same genetic defects that cause FAP (Gardner's) or HNPCC (Turcot's). (See "Screening and management strategies for patients and families with familial colon cancer syndromes".)

Most hamartomatous polyps have little malignant potential, but patients with hamartomatous polyps in the colon may be at a slightly increased risk for colon cancer. (See "Approach to the patient with colonic polyps", section on 'hamartomatous polyps' and "Screening and management strategies for patients and families with familial colon cancer syndromes".)

Men who have undergone radiotherapy for prostate cancer appear to be at increased risk for rectal cancer; the hazard ratio was 1.7 in one study [37].

HIV-infected male patients over 50 years may have a higher prevalence of colon neoplasms compared to the general population [38].

TESTS USED FOR SCREENING — Multiple tests are available as options for CRC screening. While stool-based tests improve disease prognosis by detecting early stage treatable cancers (and possibly advanced adenomas), endoscopic or radiologic tests that visualize the bowel mucosa have the potential to also prevent cancer by detecting polyps that can be removed prior to malignant transformation. Characteristics and effectiveness of available colorectal cancer screening tests are discussed separately. (See "Tests for screening for colorectal cancer: Stool tests, radiologic imaging and endoscopy".)

Tests available for screening are as follows:

Stool-based tests

  • Guaiac-based fecal occult blood test (gFOBT)
  • Immunochemical-based fecal occult blood test (iFOBT), also known as fecal immunochemical test (FIT)
  • Stool DNA panel (sDNA)

Endoscopic and radiologic examinations

  • Flexible sigmoidoscopy (FS or FSIG)
  • Optical colonoscopy
  • Double contrast barium enema (DCBE)
  • CT colonography (CTC, formerly referred to as "virtual colonoscopy")

Screening with gFOBT has been demonstrated to reduce mortality from colorectal cancer in randomized trials [39-43]. In the earliest trial, with rehydrated specimens and colonoscopy follow-up for positive results, mortality was reduced by 33 percent after annual screening and 13 years follow-up and by 21 percent after 18 years for those assigned to biennial screening [39]. Other trials report a 15 to 18 percent mortality reduction for screening with nonrehydrated gFOBT samples [40-43].

The effectiveness of other tests and procedures for prevention of CRC deaths has not been demonstrated in randomized trials, although is inferred because other screening modalities have greater sensitivity for advanced adenomas and early CRC than gFOBT. Case-control studies have demonstrated that sigmoidoscopy reduces CRC mortality by about two thirds in the area examined, which is approximately one third overall [44-46].

Fecal occult blood tests, flexible sigmoidoscopy, double-contrast barium enema, and colonoscopy with direct visualization (optical colonoscopy) have been recommended as screening options for many years. A US task force representing multiple specialty societies developed consensus guidelines in 2008 that endorse two additional screening options: computed tomographic colonography (CTC) and a panel test for stool DNA (sDNA) (table 2) [35]. The US Preventive Services Task Force also issued updated guidelines for colorectal cancer screening in 2008 and did not recommend CTC or sDNA as screening options, however [36].

COMPARISON OF TESTS AND COST-EFFECTIVENESS — Many factors influence the choice of a screening test: strength of the evidence of effectiveness, magnitude of the effect (eg, reduction in incidence or mortality from CRC), safety, convenience, comfort, availability, cost, and cost per year of life saved (cost-effectiveness).

The options for screening differ substantially in many of these dimensions (table 3A-B) [23]. Testing options for colorectal cancer screening are discussed in detail separately (see "Tests for screening for colorectal cancer: Stool tests, radiologic imaging and endoscopy".

A brief summary of relative benefits of testing options follows:

  • Stool guaiac tests have low sensitivity for polyps and relatively low specificity for significant disease, leading to workup for many false positive results. The test is non-invasive and inexpensive, but requires colonoscopy for follow-up of positive results.
  • Immunochemical stool tests are more expensive than guaiac-based tests, but have the potential to be more cost effective if fewer colonoscopies are needed for follow-up.
  • Stool DNA requires collection of an entire bowel movement and the test is expensive. The significance of false positive findings is unknown.
  • Double-contrast barium enema studies visualize the entire bowel and are relatively safe but detect one half of large (>1 cm) polyps, and abnormalities must be followed by colonoscopy.
  • Flexible sigmoidoscopy can only identify lesions in the distal 60 cm of the bowel, but can be performed with minimal patient preparation, does not require sedation, and is often performed by trained clinicians who are not specialized in gastroenterology. Abnormal findings in the distal bowel require colonoscopy for visualization of the entire colon.
  • Colonoscopy has the benefit that lesions can be removed during the same procedure, but requires conscious sedation and a vigorous bowel preparation. The procedure carries a risk of perforation and bleeding. Some polyps and cancers may be difficult to detect because of their location.
  • CT colonography also requires aggressive bowel preparation but does not require sedation and does not risk bowel perforation if findings are negative; positive findings require colonoscopy follow-up. Extracolonic findings often trigger further evaluation with little evidence of benefit. The cumulative dose of radiation, with repeated screenings, may increase cancer risk.

Charges for screening tests vary substantially. These costs are borne up front, whereas the reduction in mortality and incidence occur after several years. Insurance coverage is variable in the US. Patients with high deductible health plans are more likely to be screened with FOBT testing than with colonoscopy [47].

Most cost-effectiveness models have found that all CRC screening options are as "cost-effective" as other accepted screening tests [48-50]. Costs rise steeply with shorter screening intervals, with much smaller increases in effectiveness. There is no compelling reason to choose one option over another on the basis of cost-effectiveness alone [50].

Patient preferences have also been evaluated. One of the largest studies to evaluate procedure preferences in detail involved 614 high risk patients who underwent colonoscopy, CTC and DCBE [51]. Patients preferred colonoscopy to the other two procedures and were least satisfied with DCBE.

Another issue for population screening is the availability of the screening test. In the US, there currently is insufficient capacity to expeditiously perform colonoscopy or flexible sigmoidoscopy in all unscreened patients for whom screening would be recommended [52,53].

CHARACTERISTICS OF A SCREENING PROGRAM — Screening for CRC requires an ongoing program of appropriate testing and follow-up. One-time testing is insufficient; colon cancer incidence continues to increase with age into the ninth decade. Additionally, patients who are initially screened with tests other than colonoscopy must be willing to undergo colonoscopy for further evaluation of abnormal results and polyp removal as needed.

A robust screening program should assure that the following elements are reliably implemented:

  • Screening people at the appropriate age to identify those with an increased likelihood of disease.
  • Ongoing screening at specified intervals for people with negative initial findings.
  • Follow-up abnormal screening results with diagnostic testing to determine if polyps or cancer are present, with biopsy or excision when necessary.
  • Surveillance of high-risk people (typically those in whom a large adenomatous polyp has been found) for new lesions.

AVERAGE RISK SCREENING — Recommendations for CRC screening need to take into account multiple factors, including effectiveness, sensitivity, false-positive rate, safety, cost, cost-effectiveness, and patient preference. Two major US guidelines, from the Multi-Society Task Force and the USPSTF, were released in 2008 with somewhat differing sets of recommendations [35,36]. Additionally, the American College of Gastroenterology, (ACG, also represented on the Multi-Society Task Force) issued separate guidelines [34] that differ somewhat from the multi-society guidelines.

Multi-Society Task Force guidelines — Joint guidelines from the American Cancer Society, the United States Multi-Society Task Force on Colorectal Cancer (ACS-MSTF), and the American College of Radiology were published in 2008 (table 2 and table 4) [35]. Two additional test options, computed tomographic colonography (CTC) and fecal DNA testing, have been added to the five screening options recommended in the earlier 2001 consensus guidelines (fecal occult blood testing [FOBT], sigmoidoscopy, FOBT plus sigmoidoscopy, double contrast barium enema [DCBE], and colonoscopy).

The ACS-MSTF 2008 guidelines distinguish between tests that can detect cancers at an early treatable stage (eg, stool tests), and tests that also detect adenomas and so lead to cancer prevention (eg, structural examination of the colon, by DCBE, sigmoidoscopy, colonoscopy, or CTC). The guidelines recommend that clinicians help patients make an informed choice between the two classes of tests, and then choose specific tests within the classes. The guidelines stress that prevention, rather than early detection, should be the primary goal for most patients, and emphasize tests that are sensitive at a single point in time over repeated testing (algorithm 1).

Screening rates and preferred tests vary substantially from country to country, even in those with similar colorectal cancer rates and medical resources. In practice within the US, the frequency of colonoscopy is increasing, while use of FOBT, DCBE, and sigmoidoscopy is falling. CTC and stool DNA testing were first formally endorsed for screening in 2008, and are not yet incorporated into routine coverage by many insurance plans in the US. Medicare does not pay for screening by CTC [54].

The following recommendations are based upon the 2008 ACS-MSTF guidelines:

  • Offer screening beginning at age 50 years for average risk patients. Colorectal cancer does occur in asymptomatic average risk people under the age of 50, but infrequently enough that the costs and risks of screening outweigh the benefits [55].
  • Discontinue screening when the individual's estimated life expectancy is less than 10 years.
  • No single test is of unequivocal superiority. Incorporating patient personal preferences may increase the likelihood that screening will occur.
  • Screening should be supported by a program that assures proper follow-up of abnormal findings, and ongoing testing at identified intervals.

Early detection and prevention — Screening options that can detect both early stage colon cancer as well as precancerous lesions include (table 4):

  • Colonoscopy every ten years.
  • Computed tomographic colonography every five years.

CTC should be performed with state-of-the-art technology, and interpreted by specially trained radiologists. Follow-up optical colonoscopy is required for all polyps >10 mm, and three or more polyps >6 mm. For practical purposes, 2008 guidelines suggest that patients with any polyp >6 mm be referred for optical colonoscopy and polypectomy. Short-term CTC surveillance may be appropriate for patients with smaller polyps.

  • Flexible sigmoidoscopy every five years.

The procedure should be performed by clinicians specially trained in sigmoidoscopy, and there should be a minimum visualization of 40 cm of bowel.

  • Double contrast barium enema every five years (now infrequently used as a screening strategy).

Early detection only — Screening options that can identify early cancer include (table 4):

  • Fecal occult blood testing (FOBT) by guaiac method, performed annually
  • Fecal immunochemical-based testing (FIT) for blood, performed annually
  • Stool DNA testing performed at an uncertain frequency

Stool FOBT by guaiac should be performed by a trained technician on three consecutive stool samples using a sensitive guaiac test (eg, Hemoccult SENSA), without rehydration. Older guaiac tests (eg, Hemoccult II) are not sufficiently sensitive for screening.

The need for diet restrictions prior to FOBT is uncertain, although avoiding nonsteroidal antiinflammatory drugs for seven days (including more than one aspirin per day), and eliminating vitamin C and red meat for three days is recommended by the manufacturer. Positive tests should be followed by colonoscopy. Repeating the stool test is not adequate. Samples obtained by office rectal examination may be useful for clinical diagnosis but are not sufficient for screening.

Immunochemical-based stool testing is performed on two or three stool samples, and processed in a laboratory. It does not require diet modification. Positive tests should be followed by colonoscopy.

Stool DNA testing incorporates a panel of DNA markers and is performed on one complete stool collection that is shipped in a customized kit requiring freezing. Appropriate rescreening intervals are unknown, although the manufacturer recommends five years. Appropriate follow-up for patients with a positive screen and negative colonoscopy is unknown.

American College of Gastroenterology guidelines — The American College of Gastroenterology (ACG) 2008 guidelines recommend a "preferred" strategy, prioritizing options listed in the ACS-MSTF guidelines [34]. The ACG recommends colonoscopy as the preferred screening/prevention test and fecal immunochemical test as the preferred screening/detection test for patients who decline cancer prevention tests. Additionally, the ACG recommends initiating screening at age 45, rather than 50, for African Americans.

USPSTF guidelines — Subsequent to the ACS-MSTF 2008 guidelines, the United States Preventive Services Task Force (USPSTF) issued guidelines for colorectal cancer screening [36]. These guidelines, based on a systematic literature review and a simulation decision model, did not weigh the value of identifying premalignant lesions (prevention) over the detection of cancer (screening). The models found three screening strategies to be roughly equivalent and more effective than annual Hemoccult II, or flexible sigmoidoscopy every 5 years when performed alone. The task force found insufficient evidence of harms and benefit for CTC or fecal DNA testing.

The USPSTF recommends three screening options for adults age 50 to 75 years (table 5):

  • Annual fecal occult blood test (FOBT) with a sensitive test
  • Flexible sigmoidoscopy every 5 years, with sensitive FOBT every 3 years
  • Colonoscopy every 10 years

Why major guidelines differ — The USPSTF and ACS-MSTF guidelines are based on the same evidence but their recommendations differ. The reasons reflect differing methodologies and value judgments by the guidelines panels:

  • The ACS-MSTF gave preference to tests that can prevent cancer by detecting pre-malignant polyps over those that mainly offer early detection of cancers.
  • The ACS-MSTF was more inclusive in the tests it recommended, based on the belief that the best test is the one patients will take.
  • The USPSTF was more explicit about its process, incorporated a modeled decision analysis, and required a higher level of evidence for including a test.
  • The USPSTF was more explicit about the age to stop screening (see 'Screening in the elderly' below.

Screening in the elderly — Screening trials have included too few elderly patients to provide reliable estimates of screening effectiveness for this age group. It takes several years for screening to lower cancer rates and the decision to stop screening should depend on whether an individual patient's life expectancy justifies the risk and inconvenience of screening.

One study modeled the potential impact on life expectancy of screening colonoscopy in different age groups, based on the prevalence of benign neoplasia detected at screening colonoscopy, and estimations of the lag time from polyp to carcinoma [56]. Colonoscopy was predicted to increase survival by 0.13 years in people ≥80 years, compared to 0.85 years for people 50 to 54 years of age.

The decision whether to recommend screening for a patient over 70 years of age should depend on the patient's health status, anticipated life expectancy, risk for colorectal cancer, and personal values [57,58]. The following factors should be considered in this decision:

  • Patients with a life expectancy less than five years would not be expected to benefit from colorectal screening, since studies indicate benefit from screening accrues after five years.
  • Colonoscopy carries increased risk in the elderly, with significant complications occurring in 0.3 percent of 600 veterans aged 70 to 75 undergoing screening, compared to .01 percent for sigmoidoscopy [59]. The risks of colonoscopy increase with age and comorbidities including cardiopulmonary disease, diabetes mellitus, and history of stroke [60]. If such patients are nevertheless expected to live long enough to benefit from screening, virtual colonoscopy might be a preferred initial choice.
  • Sigmoidoscopy has reduced sensitivity in the elderly because advanced neoplasias tend to occur more proximally in this population.

Most guidelines recommend that screening for colorectal cancer stop when the patient's life expectancy is less than 10 years. The USPSTF guidelines recommend that patients over age 85 not be screened, and recommends against screening in adults 76 to 85 years, unless there are individual considerations that favor screening [59].

However, the implementation of screening in older patients appears not to be appropriately targeted, with significant numbers of healthier patients not getting screened and many patients who would not be expected to benefit receiving screening. As an example, a study of colorectal cancer screening among US veterans age 70 or older (n = 27,068) found that screening studies were done for only 47 percent of patients whose life expectancy was greater than five years but were performed for 41 percent of patients with severe comorbidity [61].

SCREENING FOR PEOPLE AT INCREASED RISK — The evidence for how high risk patients should be screened is weaker than for average risk patients. Thus, guidelines are based mainly upon arguments relating to knowledge of the biology of CRC:

  • If the patient is at risk for earlier onset CRC (eg, first degree relative with onset of CRC before age 50), screening should begin earlier.
  • If the patient is at risk for more rapid progression of disease, screening should be performed more frequently.
  • If the patient is at risk for more proximal lesions (eg, HNPCC), screening should be performed with colonoscopy.
  • If the patient is at risk for a greatly increased incidence of disease (eg, HNPCC or FAP), they should be screened with colonoscopy, the best available test.

Strategies for screening high risk patients are shown in an algorithm (algorithm 1) and discussed separately. (See "Screening for colorectal cancer: Strategies in patients with possible increased risk due to family history".)

Family history of FAP or HNPCC — Management of patients with one of several known familial colon cancer syndromes is discussed in detail elsewhere. (See "Screening and management strategies for patients and families with familial colon cancer syndromes".)

SURVEILLANCE — Surveillance refers to follow-up testing in patients who have a history of polyps, cancer, or inflammatory bowel disease. Surveillance is conceptually different than screening (which applies to patients without disease or symptoms), and is discussed on separate topics.

  • History of polyps — Once polyps have been identified by screening, the patient should be entered in a colonoscopy surveillance program. Recommendations for follow-up are discussed separately. (See "Approach to the patient with colonic polyps".)

  • History of colorectal cancer — Patients should have full visualization of the colon at the time of diagnosis to exclude synchronous cancers and polyps, and then have surveillance optical colonoscopy at regular short intervals. The surveillance interval would be determined by what is found at each colonoscopy. (See "Surveillance after colorectal cancer resection".)

IMPROVING SCREENING RATES — To maximize the impact of screening, it is not sufficient to recommend a procedure to patients. Increasing screening rates depends on numerous factors, including clinician recommendation, patient and clinician reminders, decision aids, and organization of office staff to support a program of patient education, monitoring, outreach, and follow-up [62]. (See "Overview of preventive medicine in adults".)

INFORMATION FOR PATIENTS — Educational materials on this topic are available for patients. (See "Patient information: Colon cancer screening" and "Patient information: Colonoscopy" and "Patient information: Flexible sigmoidoscopy".) We encourage you to print or e-mail these topic reviews, or to refer patients to our public web site, www.uptodate.com/patients, which includes these and other topics.

SUMMARY AND RECOMMENDATIONS

  • Screening for colorectal cancer (CRC) can identify premalignant lesions and detect asymptomatic early stage malignancy. Screening has been shown to decrease mortality from CRC. (See 'Introduction' above and 'Tests used for screening' above.)

  • The recommendations below apply to usual risk patients and require that patient history be assessed to determine if they are at increased risk for CRC. We initiate risk assessment no later than age 20 and update the information at a minimum of every five years.

Patients at sufficiently increased risk to change screening recommendations are those who have:

  • - A personal history of CRC or adenomatous polyp
  • - A genetic syndrome predisposing to CRC (ie, HNPCC, FAP)
  • - One or more first degree relatives with CRC
  • - Two or more second degree relatives with CRC
  • - IBD causing pancolitis or longstanding (>8 to 10 years) active disease

(See 'Risk factors' above.)

  • We recommend that average risk patients aged 50 and older be screened for colorectal cancer (Grade 1A). We suggest that screening be continued until the life expectancy for an individual patient is estimated as less than 10 years (Grade 2C). For most patients, it is reasonable to stop screening at age 75 years, or 85 years at the latest. (See 'Average risk screening' above and 'Screening in the elderly' above.)

  • Because a structural colon examination can lead to prevention of colorectal cancer, as well as detecting early stage disease, we suggest that patients undergo screening tests that visualize or image the colon (Grade 2B). Polyps >6 mm should be biopsied.

  The following screening strategies are options for visualizing the colon in average risk patients:

  • - Colonoscopy (optical colonoscopy) every 10 years
  • - Computed tomographic colonography (CTC or "virtual colonoscopy") every five years
  • - Flexible sigmoidoscopy (FS) every five years
  • - Double contrast barium enema (DCBE) every five years

For some patients, colon imaging or visualization may not be feasible and alternative testing (evaluation of stool samples) is an alternative and far preferable to foregoing screening. The following are options for stool testing:

  • - FOBT with guaiac reagent (gFOBT, annually on three samples)
  • - FOBT with immunochemical testing (iFOBT or FIT, annually on 2 to 3 samples)
  • - Stool DNA testing on complete stool sample (interval unknown, possibly every five years).

When guaiac FOBT tests are performed, we suggest testing with a sensitive stool guaiac reagent (eg, Hemoccult SENSA) rather than less sensitive guaiac reagents (eg, Hemoccult II) (Grade 2B).

(See 'Average risk screening' above.)

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