Bowel Cancer Screening - CancerHub New Zealand

Because of the frequency of the disease, the ability to identify high-risk groups, slow growth of primary lesions, better survival of patients with early-stage lesions, and relative simplicity and accuracy of screening tests, screening for colon cancer is being introduced in NZ for all adults aged 60 years and older, especially for those with first-degree relatives with colorectal cancer.

(Also Refer to the US PDQ summary on Colorectal Cancer Screening for more information.)

Prognostic Factors

The prognosis of patients with colon cancer is clearly related to the following:

The degree of penetration of the tumor through the bowel wall.
The presence or absence of nodal involvement.
The presence or absence of distant metastases.

These three characteristics form the basis for all staging systems developed for this disease.

Other prognostic factors include the following:

Bowel obstruction and bowel perforation are indicators of poor prognosis.[13]
Elevated pretreatment serum levels of carcinoembryonic antigen (CEA) have a negative prognostic significance.[14]

Many other prognostic markers have been evaluated retrospectively for patients with colon cancer, though most, including allelic loss of chromosome 18q or thymidylate synthase expression, have not been prospectively validated.[15–24] Microsatellite instability, also associated with HNPCC, has been associated with improved survival independent of tumor stage in a population-based series of 607 patients younger than 50 years with colorectal cancer.[25] Patients with HNPCC reportedly have better prognoses in stage-stratified survival analysis than patients with sporadic colorectal cancer, but the retrospective nature of the studies and possibility of selection factors make this observation difficult to interpret.[26]

Treatment decisions depend on factors such as physician and patient preferences and the stage of the disease, rather than the age of the patient.[27–29]

Racial differences in overall survival (OS) after adjuvant therapy have been observed, without differences in disease-free survival, suggesting that comorbid conditions play a role in survival outcome in different patient populations.[30]

Summary of Evidence

Note: Separate PDQ summaries on Colorectal Cancer Prevention; Colon Cancer Treatment; and Rectal Cancer Treatment are also available.

Evidence of Benefit Associated With Colorectal Cancer Screening

Based on solid evidence, screening for colorectal cancer (CRC) reduces CRC mortality. In addition, there is solid evidence that some CRC screening modalities also reduce CRC incidence. A meta-analysis of flexible sigmoidoscopy randomized controlled trials found that screening with sigmoidoscopy reduces all-cause mortality.

Table 1. Effect of Screening Intervention on Reducing Mortality from Colorectal Cancera

ENLARGE

Screening Intervention	Study Design	Internal Validity	Consistency	Magnitude of Effect on CRC Incidence	Magnitude of Effect on CRC Mortality	External Validity
CRC = colorectal cancer; RCT = randomized controlled trial.
aThere are no data from RCTs on the effect of other screening interventions (i.e., fecal occult blood test combined with sigmoidoscopy, barium enema, colonoscopy, computed tomographic colonography, and stool DNA mutation tests) on mortality from colorectal cancer.
Fecal Occult Blood Test (guaiac-based)	RCTs [1]	Good	Good	Likely small to none	15%–33%	Fair
Sigmoidoscopy	RCTs	Good	Good	20%–25%	About 25%; 50% for left colon	Fair
Digital Rectal Exam	Case-control studies	Fair	Good	No effect	No effect	Poor
Colonoscopy	Case-control studies; observational cohort studies that use historical/other controls; RCTs in progress	Poor	Poor	About 60%–70% for left colon; uncertain for right colon	About 60%–70% for left colon; uncertain for right colon	Fair

References

Hewitson P, Glasziou P, Watson E, et al.: Cochrane systematic review of colorectal cancer screening using the fecal occult blood test (hemoccult): an update. Am J Gastroenterol 103 (6): 1541-9, 2008. [PUBMED Abstract]

Description of the Evidence

Overview

The tables for each screening test below show the magnitude of burden for several categories of harms encountered along the screening cascade. The magnitude of harms is a combination of the frequency and severity of harm, as perceived by the patient.

Harms are defined broadly as any negative effect on individuals or populations resulting from being involved in the screening process (cascade) compared with not screening. Potential harms are organized according to the type of harm (e.g., physical, psychological and hassle/opportunity costs) and when they occur in the screening cascade (e.g., screening test/workup; screening test/workup results; surveillance and surveillance results; and early treatment and overtreatment). For example, potential harms of screening colonoscopy include harms of the screening test itself (e.g., perforation and bleeding), results of the screening test (e.g., anxiety from an abnormal result), surveillance (e.g. harms of more frequent colonoscopies), and treatment (e.g. earlier treatment or overtreatment). For other colorectal cancer screening tests, there are also harms associated with the workup (e.g. colonoscopy for positive fecal occult blood test [FOBT]). For all aspects of participating in the screening cascade, there are time/effort and opportunity costs (nonfinancial harms) for the patient. We do not include here any financial harms to the patient/family, nor any psychological harm from anticipation of future financial costs related to screening.

Table 4. Colonoscopy

Stage of Screening Cascade
	Physical	Psychological	Time/Effort, Opportunity
CRC = colorectal cancer.
Screening Test/Workup	Average 0.3% complications requiring hospitalization or resulting in death, higher with polypectomy and in older patients (fair evidence)	Percentage of people who suffer psychological distress on consideration of having colonoscopy; severity and duration (insufficient evidence)	About 38 hours (median) time required for preparation, procedure, sedation (one study, fair evidence) [1]
	Discomfort of preparation and procedure. Adverse effects of preparation. (insufficient evidence to determine magnitude and frequency)
	Complications from sedation during procedure (insufficient evidence to determine magnitude and frequency)
Screening Test/Workup Results	Increased risk of suicide and cardiovascular mortality soon after diagnosis (insufficient evidence)	Percentage of people who suffer psychological distress after receiving positive screening and/or pathological results; severity and duration (insufficient evidence)	Time and effort required to receive and understand screening test or workup results, including extra physician visits for positive tests (insufficient evidence)
Surveillance/Results	More frequent colonoscopy	Percentage of people who suffer psychological distress after receiving positive screening and/or pathological results; severity and duration (insufficient evidence)	Time and effort required to undergo colonoscopy (38 hours median, see above)
Surveillance/Results	More frequent colonoscopy		Time and effort required to receive and understand surveillance results (insufficient evidence)
Treatment (Early Treatment and Overtreatment)	Overdiagnosis and overtreatment of precursor polyps or earlier treatment of CRC (may or may not receive benefit from earlier treatment) (insufficient evidence)	Percentage of people who suffer psychological distress after undergoing overtreatment or earlier treatment without benefit; severity and duration. (insufficient evidence)	Time and effort required to receive overtreatment or earlier treatment without benefit (insufficient evidence)

Table 5. FOBT/FIT, Other Stool-Based Tests (Including Fecal DNA)

Stage of Screening Cascade
	Physical	Psychological	Time/Effort, Opportunity
CRC = colorectal cancer; FIT= immunochemical fecal occult blood test; FOBT= fecal occult blood test; N/A = not applicable.
1Workup test is colonoscopy. Descriptions of the associated harms can be found in the colonoscopy section (refer to the Colonoscopy section in the Evidence of Harms section of this summary for more information).
2Treatment harms will be the same for all screening tests.
Screening Test	None (no evidence)	Percentage of people who suffer psychological distress on consideration of having CRC screening; severity and duration (insufficient evidence)	Time and effort required to change diet (if required), collect samples, and return to appropriate facility: insufficient evidence
Screening Test Results	N/A	Percentage of people who suffer psychological distress after receiving positive screening results; severity and duration (insufficient evidence)	Time and effort required to receive and understand screening test results, including extra physician visits or communication for positive tests (insufficient evidence)
Workup1	See colonoscopy	See colonoscopy	See colonoscopy
Workup Results	N/A	See colonoscopy	See colonoscopy
Surveillance/Results	See colonoscopy	See colonoscopy	See colonoscopy
Treatment (Early Treatment and Overtreatment)2	See colonoscopy	See colonoscopy	See colonoscopy

Table 6. Flexible Sigmoidoscopy

Stage of Screening Cascade
	Physical	Psychological	Time/Effort, Opportunity
N/A = not applicable.
1Workup test is colonoscopy. Descriptions of the associated harms can be found in the colonoscopy section (refer to the Colonoscopy section in the Evidence of Harms section of this summary for more information).
2Treatment harms will be the same for all screening test.
Screening Test	Average serious complications for 0.03% of patients (fair evidence) [2]	Percentage of people who suffer psychological distress on consideration of having colonoscopy; severity and duration (insufficient evidence)	Time and effort required to perform preparation, travel to and attend screening, return to usual activities (insufficient evidence)
Screening Test Results	N/A	See colonoscopy	See colonoscopy
Workup1	See colonoscopy	See colonoscopy	See colonoscopy
Surveillance/Results	N/A	See colonoscopy	See colonoscopy
Treatment (Early Treatment and Overtreatment)2	See colonoscopy	See colonoscopy	See colonoscopy

Table 7. Computed Tomography Colonography

Stage of Screening Cascade
	Physical	Psychological	Time/Effort, Opportunity
CRC = colorectal cancer.
Screening Test/Workup	Discomfort of preparation and procedure; radiation exposure (insufficient evidence)	Percentage of people who suffer psychological distress on consideration of screening; severity and duration (insufficient evidence)	Time required for preparation, procedure (exact time and effort uncertain) (insufficient evidence)
Screening Test/Workup Results	Increased risk of suicide and cardiovascular mortality soon after diagnosis (insufficient evidence)	Percentage of people who suffer psychological distress after receiving positive screening and/or pathological results; severity and duration. (insufficient evidence)	Time and effort required to receive and understand screening test or workup results, including extra physician visits for positive tests (insufficient evidence)
Screening Test/Workup Results	Incidental extra-colonic findings [2]
Surveillance/Results	More frequent colonoscopy	Percentage of people who suffer psychological distress after receiving positive screening and/or pathological results; severity and duration (insufficient evidence)	Time and effort required to undergo colonoscopy (38 hours median, see above)
Surveillance/Results	More frequent colonoscopy		Time and effort required to receive and understand surveillance results (insufficient evidence)
Treatment (Early Treatment and Overtreatment)	Overdiagnosis and overtreatment of precursor polyps or earlier treatment of CRC (may or may not receive benefit from earlier treatment) (insufficient evidence)	Percentage of people who suffer psychological distress undergoing overtreatment or earlier treatment without benefit; severity and duration (insufficient evidence)	Time and effort required to receive overtreatment or earlier treatment without benefit (insufficient evidence)

Evidence Summary

Colonoscopy

The potential physical harms of colonoscopy include adverse effects from the preparation and adverse effects from the procedure (colonic perforation and bleeding; effects of sedation).[3–5] A systematic review of 60 studies that assessed complications of colonoscopy screening in asymptomatic patients found infrequent serious morbidity, which comprised major bleeding (0.8/1000 procedures; 95% confidence interval [CI], 0.18–1.63) and perforation (0.07/1000 procedures; 95% CI, 0.006–0.17), and only minor and short-lasting psychological harms.[6] These complications can be serious, requiring hospitalization. Colonic perforation and serious bleeding occur more often with biopsy or polypectomy, with an overall average of three to five serious complications per 1,000 procedures. The physical harm of discomfort during the procedure has been reduced by sedation, although sedation has its own potential for physical harm (magnitude and severity uncertain due to insufficient evidence).

Physical harms are also associated with further steps in the screening cascade, including diagnosis of CRC (some large ecologic studies have shown an increase in suicide soon after diagnosis) and overdiagnosis/overtreatment due to treating lesions that would never have caused the patient important problems (evidence insufficient to determine magnitude and severity).

The potential psychological harms of colonoscopy include anticipation of the procedure and anxiety while awaiting the results of biopsy reports. For people with polyps, there may be increased distress in considering oneself at increased risk of CRC (evidence insufficient). For people newly diagnosed with CRC, many will experience increased anxiety and depression for at least 6 months, as prognosis and treatment are discussed (evidence insufficient).

The harm of time/effort and opportunity costs involved in moving through the demands of the screening cascade are present throughout the process (evidence insufficient to determine frequency and severity).

FOBT/immunochemical FOBT (FIT)

The potential physical harms of fecal-based testing include the same harms as for colonoscopy for people with a positive test who have been referred for diagnostic colonoscopy.

The potential psychological harms, as well as time/effort and opportunity costs are also similar to the description above for colonoscopy (refer to the Colonoscopy section in the Evidence of Harms section of this summary for more information).[7] These harms are associated with moving through the screening cascade, regardless of the initial screening test. Although it is highly likely that these psychological harms, plus time/effort and opportunity costs, do occur, the exact frequency and severity of these harms are uncertain due to insufficient evidence.

Sigmoidoscopy

The potential physical harms of sigmoidoscopy are considerably less than those of colonoscopy, with a less intensive preparation. Serious procedural complications occur in perhaps three in 10,000 sigmoidoscopies compared with in three in 1,000 colonoscopies.[2] There is usually no sedation with sigmoidoscopy, thus again lowering the potential for complications.

The potential psychological harms of sigmoidoscopy screening, as well as the time/effort and opportunity costs of screening, are the same as given above for other screening strategies.

Computed tomography colonography (CTC)

The potential physical harms due directly to the procedure of CTC are less than either colonoscopy or sigmoidoscopy, with rare procedural complications.[2] However, CTC does involve repeated radiation exposure, with uncertain associated harms, and it also detects a number of extra-colonic incidental findings.[8–12] Incidental findings have been detected in between 40% to 98% of CTCs, with a variable number of these considered significant enough to proceed with further diagnostic testing. As there is little evidence that early detection of any of these findings could improve health outcomes for patients, these findings may be considered as harms until proven otherwise.

The potential psychological harms or time/effort and opportunity costs for CTC are similar to the descriptions above for patients moving through the screening cascade (evidence insufficient to determine frequency and severity).