`
` Digestion 2007;76:26–33
` DOI: 10.1159/000108391
`
` Published online: October 19, 2007
`
`Downloaded from http://karger.com/dig/article-pdf/76/1/26/4033192/000108391.pdf by Allen Rines on 23 October 2023
`
` New Stool Screening Tests for Colorectal
`Cancer
`
` Graeme P. Young a Stephen Cole b
`
` a Flinders Cancer Control Alliance, Flinders University, and b Bowel Health Service, Repatriation General Hospital,
` Adelaide , Australia
`
` Key Words
` Colorectal neoplasia ⴢ Fecal occult blood test ⴢ
`Guaiac-based fecal occult blood test ⴢ
`Fecal immunochemical test
`
` Abstract
` Background/Aims: The purpose of this review is to clarify
`the place of new-technology stool tests in screening for
`colorectal neoplasia. Findings: New technologies have been
`based on blood and cellular products of neoplasia. Fecal oc-
`cult blood tests (FOBTs) based on guaiac (i.e. GFOBTs) have
`been proved to be effective, but their impact on mortality
`is modest. When GFOBTs are reconfigured to provide im-
`proved sensitivity for cancer, their specificity often becomes
`unacceptable. Fecal immunochemical tests (FITs) targeting
`the human hemoglobin molecule have been shown to have
`better sensitivity for neoplasia without an unacceptable de-
`terioration in specificity. The new stool-sampling technolo-
`gies for FITs also improve population participation rates in
`screening. Most recently, quantitative FITs have become
`available; these provide flexibility for the end-user as a de-
`sired sensitivity: specificity ratio can be selected that is fea-
`sible in the context of available colonoscopic resources. A
`multi-target fecal DNA test, comprising a test for undegrad-
`ed DNA and certain common mutations, was found more
`sensitive for cancer, but not for adenoma, than the early
`GFOBTs. A more recent version including an epigenetic
`marker for the vimentin gene has further improved sensitiv-
`ity for cancer, but performance relative to GFOBT or FIT is not
`
`clear. These ‘fecal DNA tests’ have not proved to be more
`specific for neoplasia than tests that detect blood. Conclu-
`sions: FIT should replace GFOBT as the first test in two-step
`screening of large populations. It is not yet clear that tests
`targeting nonhemoglobin molecular events provide a clear
`advantage over FIT.
` Copyright © 2007 S. Karger AG, Basel
`
` Role of Stool-Based Screening Tests in the Screening
`Algorithm
`
` As the goal of screening for colorectal cancer is to re-
`duce population mortality from and/or morbidity due to
`colorectal cancer, potential screening tests require a rig-
`orous evaluation that goes beyond what is required for
`diagnostic tests being used in situations where disease
`prevalence is high [1, 2] . Screening tests are applied to
`healthy people where the risk of disease is relatively low.
` Screening tests may be applied in several contexts:
`ranging from population-based strategies where the ap-
`proach is impersonal to the personalized setting where
`screening is recommended by a doctor. No matter what
`the context, screening is by its nature a process that aims
`to increase the likelihood that affected people, while at a
`curable and usually unsuspecting stage, receive effective
`diagnosis and treatment. Screening is, therefore, a pro-
`cess with multiple phases [3] :
` • Invite and engage the person in screening
` • Perform the screening test
`
`Fax +41 61 306 12 34
`E-Mail karger@karger.ch
`www.karger.com
`
` © 2007 S. Karger AG, Basel
`0012–2823/07/0761–0026$23.50/0
`
` Accessible online at:
`www.karger.com/dig
`
` Prof. G. Young
` Department of Gastroenterology, Flinders Medical Centre
` Bedford Park
` Adelaide, SA 5042 (Australia)
` Tel. +61 8 8204 4964, Fax +61 8 8204 3943, E-Mail graeme.young@flinders.edu.au
`
`Geneoscopy Exhibit 1020, Page1
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`

`

`Table 1. Available fecal screening tests – basis for detection of neoplasia, strength of evidence and determinants of performance
`
`Detection goal
`
`Technology
`
`Strongest evidence
`for benefit
`
`Sensitivity
`determinants
`
`Specificity
`determinants
`
`Fecal blood
`
`GFOBT
`
`FIT
`
`Fecal neoplasm-
`derived DNA
`
`multitarget fecal
`DNA test
`
`population RCT –
`reduced incidence and mortality
`comparative cohort –
`better sensitivity and/or specificity
`comparative cohort –
`assessing sensitivity and specificity
`
`amount of heme in feces
`
`amount of globin in feces
`
`spectrum of DNA
`changes shed into feces
`
`dietary heme; bleeding
`nonneoplastic lesions
`bleeding nonneoplastic
`lesions
`unclear
`
`Modified from Young and Allison [1] with permission.
`
`Downloaded from http://karger.com/dig/article-pdf/76/1/26/4033192/000108391.pdf by Allen Rines on 23 October 2023
`
` • Follow up result with colonoscopy if indicated
` • Treat any lesions found
` • Repeat screening or implement follow-up surveillance
`if neoplasia found.
` There are two main choices at the point where a test is
`offered: (1) One-step testing. The diagnostic test, colo-
`noscopy, is the screening test. Selection for colonoscopy
`is based on age, and many people screened will not have
`neoplasia. (2) Two-step testing. Here, a simpler test is of-
`fered first, e.g. a fecal occult blood test (FOBT), then those
`with a positive result proceed to colonoscopy. A simple
`screening test calls attention to the likelihood of disease
`being present and serves to direct resources to those most
`likely to benefit from diagnostic and therapeutic proce-
`dures [3] .
`
` Stool Screening Tests Act by Refining the Likelihood
`that Neoplasia Is Present
` In two-step testing, the stool screening test filters out
`from the broader population those who are most likely to
`have colorectal neoplasia. This concept is embodied in
`the pretest:posttest likelihood ratio and is mathematical-
`ly expressed as test sensitivity divided by the false-posi-
`tive rate (1 – specificity) [3] . Depending on the test type
`used, various FOBT return a ratio in the range of 8–40 [1]
`meaning that those with a positive test are that much
`more likely to have colorectal cancer than those with a
`negative test.
`
` The Biological Basis of Fecal Screening Tests
`
` The usefulness of such tests depends on whether a
`colorectal neoplasm gives rise to changes in the constitu-
`ents in feces. Such constituents might derive directly
`
`from the tumor itself or be secondary to its presence. The
`processes giving rise to such products can be classified [4]
`as: leakage, secretion, or exfoliation.
` Hemoglobin, and indeed other blood-derived proteins
`such as haptoglobin and albumin, represent examples of
`leaked products. Tests have been developed based on each
`of these, although hemoglobin-based tests are by far the
`most prominent (see the section ‘Current Types of FOBT:
`Guaiac and Immunochemical Tests’ below).
` Mucins are an example of secreted products. No mu-
`cin-based test has, however, achieved significant usage.
` The products of cell exfoliation create considerable
`options for detection. Certainly, cytological studies show
`neoplastic cells to be present in feces [4] . Tests for these
`might be based on DNA (see the section ‘Nonhemoglobin
`Molecular Markers in Stool’ below), RNA or proteins. A
`recent American Gastroenterological Association Future
`Trends Committee report on emerging screening and di-
`agnostic technologies for colorectal cancer [5] identified
`a range of tests and procedures that might be appropriate.
`These include proteomics or the analysis of broad protein
`patterns, making it possible to assess small amounts of
`protein for the presence of identified cancer markers us-
`ing new protein assessment tools and computerized arti-
`ficial intelligence analysis.
` The nature of the major fecal screening tests, either
`established or under study, is summarized in table 1 . The
`efficacy of screening for colorectal cancer is supported by
`the highest level of evidence, namely randomized, con-
`trolled trials, at the population level for guaiac-based
`FOBT (GFOBT) [6–8] . Evidence supporting the other test
`technologies is not as strong, as summarized in table 1
`and further outlined below in the sections ‘Current Types
`of FOBT: Guaiac and Immunochemical Tests’ and ‘Non-
`hemoglobin Molecular Markers in Stool’.
`
` New Stool Screening Tests for Colorectal
`Cancer
`
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` Justification of New Test Development
`
` Evaluation of Test Performance
` Before considering the new developments in stool
`tests, it is worthwhile to consider whether we need new
`tests at all. To do this, we need to briefly consider what
`outcomes are important to the success of a screening pro-
`gram, i.e. what measures relate to a reduction in mortal-
`ity and/or incidence in a cost-effective and acceptable
`fashion?
` The measures of effectiveness of a screening program
`have been detailed elsewhere [1] and informative mea-
`sures can be classified as:
` • Behavioral, i.e. participation rates in screening
` • Test performance, such as sensitivity (including neo-
`plasia detection rates), specificity (including false pos-
`itives) and predictive values
` • Programmatic, namely reductions in incidence and
`mortality.
` The most immediate measurable events when screen-
`ing will be participation rate, test positivity rate, adeno-
`ma detection, downstaging of the detected cancers and,
`at a later stage, prolonged survival after treatment [1] .
`Presymptomatic detection of localized cancer will result
`in a reduction in morbidity and/or mortality [6–8] . If
`screening detects preinvasive lesions, namely dysplasia, it
`will reduce cancer incidence [9] .
` The published RCTs using GFOBT provide informa-
`tion on each of these measures; new tests can be tested
`relative to these.
`
` Performance of GFOBT
` An early measurable outcome in a screening program
`is participation , i.e. willingness of an individual offered
`screening to undertake the testing process. The RCTs of
`GFOBT have achieved rates of 53–67% when approach-
`ing the entire population, but other studies show lower
`rates [1, 6–8] . Clearly, the impact of a screening program
`on population outcomes would be greater if more people
`did a screening test [10] . It is also important to emphasize
`that FOBTs must be undertaken repeatedly for benefit to
`be shown, so ease of use is crucial.
` Rates of detection of adenomas and cancers, together
`with stage of cancer, are the next obvious outcomes. In
`themselves they are difficult to meaningfully interpret
`when expressed relative to the size of the target popula-
`tion, but if two tests are compared directly, the results
`provide a relative indication of sensitivity for the target
`lesions. Improved sensitivity for cancer will translate into
`a greater reduction in mortality.
`
` The published RCTs using the standard GFOBT,
` Hemoccult, have observed modest population mortality
`reductions (from colorectal cancer) of 14–21% when ana-
`lyzed on an intention-to-screen basis [6–8] . This modest
`impact is a direct consequence of the low sensitivity of
`Hemoccult for cancer, estimated in a range of studies to
`be around 33% and no greater than 50% [1, 11] . Clearly, a
`more sensitive test seems likely to have a greater impact
`on mortality as a larger number of cancers will be de-
`tected by screening.
` Cumulative incidence rates for colorectal cancer did
`not differ between the controls and screened groups in
`the RCTs using GFOBT after 13 years of follow-up. How-
`ever, after 18 years of follow-up, the Minnesota study ob-
`served a significant impact on incidence whether screen-
`ing was annual or biennial [9] . It seems likely that the
`higher sensitivity of rehydrated Hemoccult and the resul-
`tant higher colonoscopy rate [6] has resulted in a better
`detection (and thus removal) of adenomas. Obviously,
`improved sensitivity for adenomas would result in a
`greater impact on incidence.
` Unfortunately, increasing the sensitivity of GFOBT
`leads to a marked deterioration in specificity [11] and this
`would also increase cost of the program as the colonos-
`copy rate is a major determinant of cost.
` To summarize, we need new tests because there is
`much room to improve participation rates of those being
`invited to screen, to improve sensitivity for cancer, to im-
`prove sensitivity for adenomas, and to achieve the im-
`proved sensitivity without unacceptable deterioration in
`specificity.
`
` Current Types of FOBT: Guaiac and Immunochemical
`Tests
`
` The fact that microscopic bleeding may arise from
`curable cancers, and adenomas, provides the basis for
`screening using an FOBT [3] . However, the biology of
`bleeding is complex and the different FOBT technologies
`now available are influenced by the biological fate of
`blood in the gut [9] .
` Available FOBTs are based on two principal quite dif-
`ferent technologies: chemical or immunochemical detec-
`tion of one or other component of blood. The major fea-
`tures of these tests are outlined in table 2 [1, 12] .
`
` Chemical FOBT
` The chemical tests (e.g. Hemoccult II) react to the per-
`oxidase capacity inherent in the heme molecule [13] .
`
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`Table 2. Characteristics of different types of FOBT [1, 12]
`
`Type of
`FOBT
`
`Chemical basis
`
`Diet restrictions
`
`Drug inter-
`ference
`
`Site of occult
`bleeding detected
`
`Specificity for
`neoplasia1
`
`Sensitivity for
`cancer1
`
`Chemical
`(GFOBT)
`
`guaiac detects peroxidase
`activity of heme
`
`Immuno-
`chemical
`(FIT)
`
`anti-human hemoglobin
`antibody detects globin
`
`required: red meats;
`possibly certain
`raw plant foods2
`none required
`
`vitamin C,
`possibly
`NSAIDs3
`none
`
`rectum > colon >
`stomach (in decreasing
`order of sensitivity)
`colon and rectum
`
`90–98% depending
`on test brand and
`usage
`around 95% depend-
`ing on sensitivity
`level chosen4
`
`35–67% with one-time testing;
`over 80% with repeated testing
`
`65–90% with one-time testing;
`unclear for repeated testing
`
`Presented in modified form with permission [1].
`1 Indicative estimates only.
`2 Delaying development for 72 h minimizes interference from plant foods and avoids need for their restriction with standard Hemoccult II. Red meats
`must be restricted when using a more sensitive GFOBT [12].
`3 Low-dose aspirin is not a problem, but therapeutic doses such as for rheumatic disorders may.
`4 Tests generally provide a qualitative result, but some newer FITs can be quantifiable.
`
`Guaiac is the reagent in most chemical tests. These
`GFOBTs react to any peroxidase in feces (e.g. plant per-
`oxidases or heme in red meat) and are affected by certain
`chemicals (e.g. vitamin C). GFOBTs may detect bleeding
`from any site in the gastrointestinal tract, including
`stomach [13] , as heme remains relatively stable during
`transit.
` GFOBTs that are more sensitive than Hemoccult, e.g.
`Hemoccult II Sensa, have been developed to improve sen-
`sitivity; in practice they appear to almost double sensitiv-
`ity. While valuable, this is unfortunately at a cost of de-
`creased specificity [11] .
`
` Fecal Immunochemical Tests
` Fecal immunochemical tests (FITs) use antibodies
`specific for human globin. This technology provides sev-
`eral advantages. It is not affected by diet or vitamin C [5,
`13, 14] . FITs as a class are subject to less variability in
`positivity rate than the sensitive GFOBT [15] . FITs are
`also highly selective for occult bleeding of colorectal ori-
`gin because globin is rapidly degraded by digestive en-
`zymes [13] . These provide specificity advantages over
`GFOBT, especially the more sensitive GFOBT.
` These improvements in specificity have, depending on
`the brand of FIT, been combined with improvements in
`fecal sampling; these are discussed elsewhere in detail
` [12, 14, 16] . FITs have also been developed to provide for
`large scale development in the laboratory where quality
`assurance of test development is much easier to monitor
`and control. Laboratory development is preferred in
`many countries, especially for mass screening when
`many tests must be done and quality assurance is vital.
`
` Comparisons of GFOBT with FIT
` It is beyond the scope of this review to fully analyze all
`studies comparing these technologies. Several studies
`have been selected to demonstrate key issues about these
`two quite different technologies.
` Population participation is essential for cancer detec-
`tion [3] . FIT technology simplifies the testing process, re-
`moves the need for diet and drug restrictions, provides
`for preferred and more acceptable stool-sampling meth-
`ods such as brushes or probes rather than a wooden spat-
`ula, and is achieved while collecting fewer fecal samples.
`Most branded versions of FIT require fewer than three
`fecal samples, the recommended number for GFOBT. Re-
`moval of dietary restrictions has been shown to enhance
`participation in screening with FIT relative to GFOBT, in
`one study by 28% [10] . Changing to a brush-sampling
`method also simplifies the process and enhances partici-
`pation by 30%. Together, these two advances increase
`population participation by 66% [10] .
` A study of over 7,000 people undergoing screening in
`California was the first to provide a large-scale compari-
`son of two types of GFOBT with an FIT [11] . It showed
`that a sensitive GFOBT, Hemoccult Sensa, doubled detec-
`tion rate of Hemoccult II for cancer but required almost
`5 times as many colonoscopies to achieve this. An FIT, no
`longer available commercially, also achieved double the
`sensitivity but with only a doubling of the colonoscopy
`rate. FITs provide for an improved sensitivity/specificity
`ratio; in other words, they can achieve better sensitivity
`without an unacceptable deterioration in specificity.
` More recently, a new brush-sampling FIT (InSure) has
`been directly compared with Hemoccult Sensa in several
`
` New Stool Screening Tests for Colorectal
`Cancer
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`Increasing likelihood of neoplasia
`
`Cut-off point
`(selected by
`manufacturer)
`
`Frequency
`
`Stool hemoglobin concentration
`
` Fig. 1. Theoretical distribution of fecal hemoglobin concentra-
`tions in a target screening population showing a tail to the right
`as those with pathology will have higher concentrations than
`those with a normal colon. As the hemoglobin concentration in-
`creases, there is a continuous increase in the likelihood of finding
`neoplasia. Qualitative tests are set to react at a given hemoglobin
`concentration and so the likelihood of neoplasia varies with the
`cut-off selected. The proportion of the population falling in the
`grey-shaded area will be those who are colonoscoped.
`
`clinical and screening cohorts undertaking paired sam-
`pling of stools [14] . The FIT returned a true-positive re-
`sult significantly more often in those with cancer (n = 24,
`87.5 vs. 54.2%) and in those with significant adenomas
`(n = 61, 42.6 vs. 23.0%). The false-positive rate for any
`neoplasia was marginally higher with the FIT than the
`GFOBT (3.4 vs. 2.5%, 95% CI of difference 0–1.8%), while
`positive predictive values were 41.9 and 40.4%, respec-
`tively.
` A recent study involving 1,486 subjects in Scotland
`further supports the observations that specificity remains
`acceptable with FITs even though they have improved
`sensitivity [17] .
` Table 2 shows performance estimates of the different
`types of the FOBT, i.e. GFOBT and FIT. As a general rule,
`FITs are at the more sensitive end of the range while
`GFOBTs vary widely across the range.
` Obviously, FITs overcome most of the disadvantages
`presented by GFOBT, are superior to GFOBT in terms of
`participation as well as performance and should replace
`GFOBT in two-step screening [14, 16] .
`
` Quantitative Immunochemical Tests
`
` Several of the latest FITs, namely OC-Micro and
` InSure, provide for quantification of fecal hemoglobin
` [18, 19] . The relationship between fecal hemoglobin con-
`centration and pathology has been explored in these
`studies and gives more insight into strategies for manag-
`ing FIT-based screening programs. Several interesting
`guiding principles emerge from these studies:
` • As pathology progresses, hemoglobin concentration
`increases (cancers bleed more than advanced adeno-
`mas which bleed more than small adenomas).
` • Patients with advanced adenomas do show higher fe-
`cal hemoglobin concentrations than those without
`neoplastic pathology.
` • Quantification enables one to select a cut-off corre-
`sponding to a particular chosen sensitivity/specificity
`ratio.
` These studies clearly show that the greater the amount
`of marker present in the stools, the more likely is neopla-
`sia to be present. If we represent a theoretical distribution
`of fecal hemoglobin concentrations in a target population
`( fig. 1 ), we would find that as the hemoglobin concentra-
`tion increases there is a continuous increase in the likeli-
`hood of finding neoplasia. Qualitative FOBT are designed
`to return a positive at a set hemoglobin concentration, the
`‘cut-off’ that defines positivity. Cut-offs vary between
`
`manufactured tests and so the likelihood of neoplasia be-
`ing present varies according to where it is on the curve in
` figure 1 . Qualitative tests fail to provide for flexibility in
`varying the cut-off. The same principle should apply for
`any other molecular marker in feces unless it is totally
`specific for neoplasia.
` Several groups [18, 19] have shown how quantification
`provides flexibility by constructing an ROC curve, ex-
`pressing the relationship between sensitivity and speci-
`ficity at different hemoglobin concentrations. In practice,
`the hemoglobin cut-off used to trigger colonoscopy can
`be adjusted to correspond to a particular chosen sensitiv-
`ity:specificity ratio. No longer is the test performance as
`set by a manufacturer important, since the flexibility pro-
`vided by quantification allows those running screening
`programs to select whatever sensitivity:specificity ratio
`they want, while knowing that the lower the cut-off he-
`moglobin concentration selected, the greater is the chance
`of detecting significant neoplasia.
` An even simpler way to apply this flexibility is to
`choose a hemoglobin cut-off that delivers a positivity rate
`that is manageable in terms of the resultant colonoscopy
`rate. For instance, if it is considered that 5% of the target
`population can be realistically colonoscoped, then the
`cut-off can be selected to achieve that. The real concern
`is what constitutes an acceptable rate. We know from
`
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`RCTs using the GFOBT Hemoccult II that a significant
`impact on mortality was achieved with a positivity rate
`of just 2% [7, 8] . So, we can be confident that working with
`a positivity rate higher than that will achieve better can-
`cer detection and be more likely to deliver a similar or
`better reduction in mortality.
` To summarize, the advantage of fecal hemoglobin
`measurement is that it returns full control of sensitivity
`and specificity to the end-user [3] who can establish the
`level of fecal hemoglobin that would trigger colonoscopy.
`At the population level, such an approach allows optimi-
`zation of the test specificity:sensitivity ratio, so adapting
`the colonoscopy rate to the facilities and resources avail-
`able for screening.
`
` Nonhemoglobin Molecular Markers in Stool
`
` Detection of molecular or genetic events that either
`cause cancer or else reflect development of neoplasia
`could theoretically be useful in selecting who undergoes
`colonoscopy. Because of the molecular heterogeneity of
`DNA in neoplasms, selecting the best panel of markers
`represents a challenge.
` The first large-scale evaluation of the value of fecal
`DNA testing (using a 21-mutation multitarget panel) as a
`first-step test in two-step screening for colorectal cancer
`has recently been reported [20] . This version of the stool
`DNA test (PreGen Plus) is costly (in excess of USD 400)
`relative to GFOBT and FIT (up to USD 30) and requires
`a somewhat cumbersome stool collection that needs to be
`rapidly delivered to the processing laboratory [21] . The
`comparator tests were colonoscopy as the diagnostic ref-
`erence standard and Hemoccult II (unhydrated) as the
`proven first-step screening test [20] . Results were ana-
`lyzed in a subgroup of 2,507 which included all subjects
`found to have neoplasia as well as a range of subjects with
`normal colon or benign disease. The cancer detection
`rate using the fecal DNA panel compared to Hemoccult
`II was 16 of 31 (52%) versus 4 of 31 (13%, p = 0.003), re-
`spectively. While sensitivity was greater than that with
`Hemoccult II, it was lower than would be hoped for and
`the reported sensitivity of Hemoccult II was substantial-
`ly lower than that reported in other studies for one-time
`testing [10] . The reasons for this seem likely to relate to
`the fact that Hemoccult II tests were developed at many
`different sites rather than at a centralized site paying full
`attention to quality assurance. The performance of both
`tests for detecting advanced adenomas was similarly dis-
`appointing: 61 of 403 (15.1%) for fecal DNA versus 43 of
`
`403 (10.7%) for Hemoccult II. In those with negative (no
`finding of adenoma or cancer) colonoscopy, 5.6% had
`tested positive on fecal DNA compared to 4.8% on He-
`moccult II (specificities of 94.4 and 95.2%, respectively).
`Fecal DNA testing did not identify the majority of neo-
`plastic lesions found at colonoscopy.
` Another recent study failed to find an association be-
`tween K-ras mutations in the stool and development of
`colorectal cancer [22] .
` In this format (i.e. as PreGen Plus [20] ) the fecal DNA
`test has not met expectations of sensitivity or specificity,
`and while it might be more sensitive for cancer than
` Hemoccult II, it is quite unclear as to whether it repre-
`sents an advance over the newer FOBT types and espe-
`cially FIT.
` Further enhancements of fecal DNA testing are now
`emerging. These take advantage of certain epigenetic
`changes that can characterize colorectal neoplasia togeth-
`er with improved methods for stabilization of DNA. These
`two approaches have been combined in a new-generation
`fecal DNA test, PreGenPlus v2, where the main compo-
`nents of the test comprise an optimized method for detect-
`ing undegraded DNA (‘DIA’, a characteristic of neoplasia)
`together with a marker for methylation of the vimentin
`gene [23] . In a clinical cohort of 40 patients with cancer,
`the DIA component returned a 65% sensitivity, the vimen-
`tin test a 73% sensitivity and together an 88% sensitivity.
`At this stage, the performance in screen-detected cancers
`is not clear, nor has performance relative to FIT or GFOBT
`been studied. It is intriguing that a test based on methyla-
`tion might achieve such a sensitivity, since tumors bearing
`the so-called methylation genotype, the CIMP pathway,
`seem likely to constitute no more than 20% of all colorec-
`tal neoplasia [24] . Clearly, there is overlap between mo-
`lecular pathways of colorectal oncogenesis.
` Specificity of the PreGenPlus v2 test has been deter-
`mined in 122 people with a normal colon [23] . Combined
`specificity was 82%. This is not an improvement over FIT
`and is clearly inferior. This finding further demonstrates
`that DNA-based tests are not necessarily specific for neo-
`plasia. The explanation for this is not clear, but the most
`likely possibility is that some molecular lesions emerge
`before focal lesions become obvious at colonoscopy.
`Whether such ‘occult’ lesions are likely to progress at a
`later stage is unknown. If they were, this might represent
`an argument for more intensive colonoscopic surveil-
`lance of such individuals, but this is pure speculation at
`this stage.
` To summarize, fecal DNA tests require much more
`work before it is clear what the best markers are, how
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`these compare to GFOBT and FIT, and what the relative
`costs will be.
` Nonetheless, it seems most likely that if stool tests can
`be improved, the new generation stool screening tests will
`emerge from discovery of new markers that improve sen-
`sitivity or specificity relative to FIT. DNA-based tests will
`continue to improve, but RNA-based and proteomic tests
`might also prove valuable.
`
` Conclusions
`
` The benefits of stool screening tests are several: they,
`particularly GFOBT, are proven by RCTs to have an im-
`pact on mortality and incidence, and they are acceptable
`to a majority of the population in that people will under-
`take such testing. Stool tests provide a simple introduc-
`tion into the screening algorithm – they serve to profile
`risk for neoplasia and direct those more likely to have
`neoplasia to receive colonoscopy.
` There are several disadvantages: fairly frequent testing
`seems to be necessary and sensitivity for incident lesions
`still leaves room for improvement whether they are based
`on blood or tumor DNA. No stool test is specific for neo-
`plasia.
` Recent developments in FITs, namely quantification,
`provide for a flexible approach to screening in that they
`
`do not commit the end-user to a particular sensitivity:
`specificity ratio and they have improved capacity to de-
`tect adenomas compared with GFOBT. As they are also
`more acceptable to people offered screening, FIT should
`replace GFOBT for screening. Perhaps, quantification
`represents the ultimate refinement of FIT and there might
`not be much room for further improvement.
` Fecal DNA tests, especially the latest versions, need
`further evaluation in screening cohorts before we can be
`confident of their ability to detect cancers relative to FIT.
`They do appear to be more sensitive for cancer than the
`GFOBT Hemoccult II. As yet, fecal DNA tests have not
`been shown to have any advantage for adenoma detection
`and they are no more specific than GFOBT.
` The challenge for fecal screening tests is to provide
`more reliable identification of those who might have an
`advanced adenoma in the colon. This would more effec-
`tively target colonoscopy to this group and reduce indis-
`criminate colonoscopic screening of everyone considered
`to fall within the at-risk age range. Fecal molecular tests
`have the potential to achieve this, but the ideal marker, or
`panel of markers, is yet to be identified.
`
` Disclosure Statement
`
` G. Young is a recipient of research funds from Enterix Inc.
`
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`
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