D i a g n o s i n g c o l o r e c t a l c a n c e r
`
`Diagnosing Colorectal Carcinoma: Clinical
`and Molecular Approaches
`
`J. Milburn Jessup, MD
`Herman R. Menck, MBA
`A. Fremgen, PhD
`D.P. Winchester, MD
`
`Introduction
`Colorectal carcinoma is the fourth most
`prevalent carcinoma and second most
`frequent cause of death from cancer in
`the United States, with an estimated
`131,200 new cases and 54,900 deaths in
`1997.1 Although the death rate from large
`bowel cancer may be decreasing slightly,
`it still remains a health risk that consumes
`national resources and creates consider-
`able personal suffering. Dietary modifica-
`tion may decrease the neoplastic trans-
`formation potential of bowel mucosa,2
`but the widespread adoption of low fat,
`high fiber diets will not eliminate totally
`the risk of large bowel cancer. The con-
`sumption of aspirin3,4 or other nons-
`teroidal anti-inflammatory drugs5 may also
`reduce the risk of developing the adeno-
`matous polyps that precede large bowel
`cancers. However, not all patients benefit
`
`Dr. Jessup is an Associate Professor of Surgery in the
`Department of Surgery at New England Deaconess
`Hospital and Harvard Medical School, Boston,
`Massachusetts.
`Mr. Menck is the Manager of Clinical Information
`Systems for the Commission on Cancer of the
`American College of Surgeons in Chicago, Illinois.
`Dr. Fremgen is the Associate Manager of Clinical
`Information Systems for the Commission on Cancer of
`the American College of Surgeons in Chicago, Illinois.
`Dr. Winchester is Professor of Surgery at Northwestern
`University Medical School, Director of the Cancer
`Department at the American College of Surgeons in
`Chicago, and Chief of Surgery at Evanston Hospital in
`Evanston, Illinois.
`This work funded in part by grant PO1 CA44704 from
`the National Cancer Institute, National Institutes of
`Health, Bethesda, MD, and grant CCG #252E from
`the American Cancer Society, Atlanta, Georgia.
`
`from these chemoprevention strategies
`and some may have deleterious side ef-
`fects. Recently, fecal occult blood testing
`(FOBT) and large bowel endoscopy have
`been found to detect cancers at an earlier
`stage and decrease the formation of col-
`orectal carcinomas. Also, the recent iden-
`tification of specific genetic mutations
`that cause two different types of inherited
`colorectal carcinoma suggests that in the
`near future early diagnosis will be possi-
`ble through blood or stool tests. As a re-
`sult, considerable enthusiasm now exists
`that both the rate of earlier diagnosis and
`the outcome of colorectal carcinoma will
`be improved.
`This review first assesses the com-
`mon patterns of presentation of col-
`orectal carcinoma, then summarizes the
`current status of clinical diagnostic
`methodology, and finally outlines the fu-
`ture potential of molecular diagnostic
`tests. Critical to the successful application
`of molecular diagnostic tests is an appro-
`priate understanding of the clinical back-
`ground within which the tests will be
`used. Initially, this review focuses on the
`clinical presentation of colorectal carci-
`noma, then considers the genetic and bio-
`logic causes of colorectal carcinoma. Any
`molecular approach to diagnosis must ex-
`plain the range of clinical and pathologic
`features involved in the manifestations of
`the disease at presentation. Currently,
`more patients are diagnosed because they
`develop signs or symptoms of colorectal
`cancer than are identified in an asympto-
`matic state. A major goal is to increase
`the proportion of patients who are diag-
`
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`Table 1
`Conditions Associated with Colorectal Carcinoma
`
`Clinical
`Rectal bleeding (occult or clinical)
`Abdominal, pelvic, or back pain
`Obstruction or perforation
`Inflammatory bowel disease
`Pelvic radiation
`
`Genetic
`History of colorectal carcinoma
`History of adenomatous polyps
`History of two or more first-degree relatives with bowel cancer
`Familial adenomatous polyposis, hereditary nonpolyposis colon cancer,
`or variant syndromes
`History of breast, ovarian, or endometrial carcinoma
`
`nosed while they are asymptomatic be-
`cause these patients present at an earlier
`stage that is more amenable to cure.6
`
`Common Patterns of Clinical
`Diagnosis
`The clinical and genetic conditions associ-
`ated with the development of colorectal
`carcinoma (Table 1) represent the situa-
`tions in which the clinician should consid-
`er the diagnosis of colorectal carcinoma.
`Although it is difficult to identify the frac-
`tion of patients who are symptomatic at
`diagnosis, analysis of a large number of
`patients who are diagnosed in hospitals
`across the country is informative because
`it demonstrates the distribution of stage
`at diagnosis. The National Cancer Data
`Base (NCDB), a national cancer manage-
`ment and outcomes data base that is a
`joint effort of the American Cancer Soci-
`ety and the American College of Sur-
`geons,7 currently captures more than 50
`percent of the estimated new cases of
`cancer in the United States and is an ex-
`
`cellent starting point for an analysis of the
`patterns of care and outcome for patients
`with cancer. Data on the interaction of
`age, ethnicity, site of primary carcinoma,
`and stage at presentation are presented in
`Table 2. As reported earlier in a study of
`colon cancer,8 patients over the age of 70
`years are more likely to present with
`stage I or II disease than are younger pa-
`tients. This trend is also present in rectal
`cancer, in which 62 percent of patients
`over 80 years of age have stage I or II dis-
`ease compared with 50 percent for those
`patients who are less than 50 years old
`and 53 percent for those who are between
`50 and 60 years old (Table 2). Ethnicity
`is another significant factor because
`African Americans are less likely to pre-
`sent with stage I or II colon or rectal can-
`cer than are non-Hispanic whites (Table
`2). Hispanics are also slightly less likely to
`be diagnosed with stage I or II colorectal
`carcinoma than are non-Hispanic whites
`(Table 2). However, Asians have a pat-
`tern of stage at diagnosis similar to that of
`non-Hispanic whites (data not shown),
`
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`Table 2
`Distribution of Adenocarcinoma of the Colon and Rectum
`by AJCC Stage, Age at Diagnosis, and Ethnicity of Patients
`Diagnosed in 1993 at Hospitals
`Participating in the National Cancer Data Base
`
`Site and Category
`
`I-II
`
`% Distribution by Stage
`III
`
`Age
`
`Colon
`< 50
`50–59
`60–69
`70–79
`≥80
`Subtotal
`
`Rectum
`< 50
`50–59
`60–69
`70–79
`≥80
`Subtotal
`
`Ethnicity
`
`Colon
`Non-Hispanic white
`Hispanic
`African American
`
`Subtotal
`
`Rectum
`Non-Hispanic white
`Hispanic
`African American
`
`Subtotal
`
`44
`47
`53
`57
`59
`
`50
`53
`58
`59
`62
`
`55
`51
`48
`
`58
`53
`54
`
`27
`27
`26
`25
`25
`
`33
`30
`27
`26
`22
`
`25
`29
`27
`
`27
`27
`25
`
`IV
`
`29
`26
`21
`19
`16
`
`17
`17
`15
`15
`16
`
`20
`20
`25
`
`15
`20
`21
`
`Total %
`
`Number of
`Cases
`
`100
`100
`100
`100
`100
`
`100
`100
`100
`100
`100
`
`100
`100
`100
`
`100
`100
`100
`
`2,503
`4,130
`9,112
`12,871
`8,661
`
`37,277
`
`1,338
`2,406
`4,273
`4,579
`2,238
`
`14,834
`
`32,463
`680
`3,087
`
`36,230
`
`11,731
`372
`950
`
`13,053
`
`AJCC = American Joint Committee on Cancer.
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`and the sample of Native Americans is
`too small to draw any conclusions about
`their stage at presentation. The data in
`the NCDB do not reveal any significant
`effects of median income, region of the
`country, or type of hospital on the stage
`of disease at diagnosis (data not shown).
`As a result, these data from the NCDB
`suggest that age and ethnicity are impor-
`tant factors to consider in the diagnosis of
`colorectal carcinoma.
`IMPORTANCE OF AGE
`Age has two contrasting effects on the
`diagnosis of colorectal carcinoma.
`Young (less than 40 years old) patients
`have a worse outcome than middle-aged
`patients, whereas older (more than 70
`years old) patients present with earlier
`stage of disease. Bacon9 first reported
`that colorectal carcinoma is diagnosed
`before age 40 in 2 to 6 percent of all col-
`orectal carcinoma patients. The delay in
`attributing symptoms to a possible col-
`orectal cancer may contribute to the
`worse outcome.10,11 Although several
`series indicate that there is a worse out-
`look for patients who develop colorectal
`carcinoma before the age of 40,12-17 two
`series18,19 suggest that younger patients
`have the same survival as older patients,
`possibly because the distribution of pa-
`tients with stage III and IV disease was
`similar to that of the older patients in
`their series.
`The outcome of younger patients
`may be worse because they present with
`more advanced disease or disease with a
`poorer histologic grade of differentiation.
`Several authors10,12-16 have found that
`younger patients present with more nodal
`or visceral metastases than do older pa-
`tients, as is the case with the current data
`from the NCDB (Table 2). However, the
`data of others13,14,17,20 suggest that the out-
`come of younger patients is worse than
`that of older patients, even when matched
`by stage.
`The frequency of more advanced
`disease in younger patients may result
`
`from longer delays in diagnosis compared
`with older patients; however, the fre-
`quency of rectal bleeding or abdominal
`pain in these young patients is similar to
`that in older patients. Further, Adkins et
`al16 observed that eight of the 45 patients
`were found incidentally during evaluation
`for other problems, which suggests that
`the potential delay in detecting a cancer
`from the onset of symptoms was less than
`three months. Similarly, in other stud-
`ies18,20 there was no significant difference
`in symptom duration between young and
`old patients. In summary, there is a con-
`sensus that the disease presents at a more
`advanced state
`in younger patients.
`Therefore, patients who develop colorec-
`tal cancer before age 40 in the absence of
`a defined genetic syndrome, such as famil-
`ial adenomatous polyposis or hereditary
`nonpolyposis colonic cancer, may still
`have an accelerated rate of mutations that
`may provide clues to the analysis of the
`genetic mechanisms that cause sporadic
`colorectal carcinoma.
`Older patients with colorectal cancer
`are defined as older than 75 or 80 years at
`the time of diagnosis. Comorbid disease
`and type of presentation may produce a
`worse outcome. The series of Payne et
`al,21 Wise et al,22 and Hobler23 suggest that
`sepsis and complications of surgery may
`occur more frequently in the elderly pop-
`ulation. However, Arnaud et al24 showed
`that the postoperative five-year survival
`rate of older patients was similar to that
`of younger patients. In addition, the
`three-year23 and five-year21 cancer-specif-
`ic survivals of patients over the age of 75
`were the same as that of younger pa-
`tients. Interestingly, several authors sug-
`gested that more right-sided cancers arise
`in the elderly than in the slightly younger
`population.18,21 The elderly seem to have
`a slightly increased frequency of emer-
`gency operations, since 7.4 percent of old-
`er patients required emergency surgery,
`compared with four percent for patients
`younger than 75 years.21 Thus, the biolog-
`ic behavior of cancers is not likely to be
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`more aggressive in older patients than in
`patients between 40 and 70 years old.
`
`ETHNICITY AS A DIAGNOSTIC FACTOR
`Ethnicity may be associated with an in-
`creased frequency of advanced cancer at
`diagnosis in African Americans. Thomas
`et al25 suggest that inner-city blacks are
`diagnosed with colorectal carcinoma at
`an earlier age than white patients, and
`that this trend is significantly greater in
`black males than in white males. Boring
`et al26 have reported that there has been
`a significant increase in cancer-specific
`death rates in both black men and
`women for colorectal cancer compared
`with white men and women over the last
`30 years. In fact, the cancer-specific
`death rate declined in white men and
`women, whereas it increased in black
`men and women by 47 and 16 percent,
`respectively.26 Interestingly, when inci-
`dence rates are stratified by educational
`level and socioeconomic status, the inci-
`dence of cancer of the colon and rectum
`is higher for whites than for blacks for
`each stratification.26 As in the current
`NCDB data, Boring et al26 observed a
`trend in which the frequency of localized
`cancer at diagnosis is lower in blacks (30
`percent) than in whites (36 percent).
`Thus, the poorer outcome may be attrib-
`utable to more limited access to care.
`Weaver et al,27 reporting their experi-
`ence over a 10-year period at Meharry
`Medical College, found that their black
`patients tended to present with more ad-
`vanced disease than did those observed
`by Boring et al.26 Their experience may
`also reflect limited access to health care
`systems. A major challenge for improv-
`ing early diagnosis is to increase the pro-
`portion of stage I and II colorectal can-
`cers diagnosed in African Americans.
`
`PRESENTING SYMPTOMS AND SIGNS
`The symptoms and signs of carcinoma of
`the colon and rectum are rectal bleeding
`
`(either gross blood in the stool or a gua-
`iac-positive reaction on digital rectal ex-
`amination), abdominal pain, change in
`bowel habits, nausea, vomiting, abdomi-
`nal distention, weight loss, fatigue, and
`anemia. Rectal bleeding may be associ-
`ated with an improved outcome, possi-
`bly because it prompts earlier diagnosis.
`Various authors28-31 have observed that
`rectal bleeding as a presenting symptom
`was associated with a better overall sur-
`vival in univariate analyses, but when
`rectal bleeding was analyzed in multi-
`variate analysis in which it was corrected
`for stage and site, it either had no ef-
`fect29,31 or became less important as an
`independent prognostic variable.28 Simi-
`larly, Wiggers et al32 found that only 19
`percent of patients who presented with
`rectal bleeding died of disease compared
`with 33 percent of patients who did not
`present with rectal bleeding (P=0.017).
`Cappell and Goldberg33 observed that
`rectal bleeding was 2.8 times more
`prevalent at the time of diagnosis in ear-
`ly stage I lesions than in stage IV can-
`cers. Also, Graffner and Olsson34 report-
`ed that rectal bleeding was more
`frequently associated with rectal (50 per-
`cent) than colon (14 percent) cancer.
`Thus, rectal bleeding may be associated
`with early stage lesions (perhaps be-
`cause early lesions are more vascular-
`ized than more advanced lesions) and, as
`a result, may carry a better prognosis.
`Thus, blood on the stool on digital rectal
`examination, on guaiac test, or by history
`must be further evaluated and not dis-
`missed as caused by hemorrhoids.
`Abdominal pain is another symptom
`that may lead to the diagnosis of large
`bowel cancer. Two types of abdominal pain
`are caused by cancer of the colon or rec-
`tum. The first is cramping or colicky pain
`associated with complete or partial bowel
`obstruction. Although uncommon in rec-
`tal cancer, it may be a presenting symptom
`in colonic cancer. This symptom may be
`best considered as representing the clini-
`cal syndromes of obstruction or perfora-
`
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`tion that are discussed later. Wiggers et
`al32 identified abdominal pain and change
`in bowel habits as significant covariates in
`their multivariate analysis of patients with
`colorectal carcinomas.
`Either pelvic pain or tenesmus may
`be a symptom of a locally advanced rectal
`cancer and may be caused by involve-
`ment of peripheral nerves.35 Such a local-
`ly advanced rectal cancer may be suc-
`cessfully treated with a multimodality
`approach. However, pain is more likely
`to be associated with a stage III than a
`stage I lesion and, as a result, may have a
`worse prognosis. Other complaints, such
`as nausea, vomiting, anorexia, and weight
`loss of more than 5 kg, are uncommon at
`presentation but are more likely to be as-
`sociated with advanced than early stage
`cancers.33
`Finally, hemorrhoids at presentation
`may not be associated with survival but
`may be associated with early stage can-
`cers of the colon.33 These data reinforce
`the need to evaluate the entire colon
`when a patient presents with rectal bleed-
`ing and hemorrhoids.
`Anemia secondary to microscopic
`bleeding (e.g., iron deficiency anemia),
`especially from a right-sided colonic can-
`cer, may be a bad prognostic factor, par-
`ticularly when it is associated with fatigue
`and weight loss because it is associated
`with a fivefold increased risk of metastat-
`ic disease.33
`In summary, rectal bleeding may be
`associated with early stage disease and
`better survival. Complete or partial bow-
`el obstruction often adversely affects out-
`come. Constitutional signs and symp-
`toms–such as general malaise, weight
`loss, and profound anemia–are often as-
`sociated with advanced disease and re-
`flect the poor outcome of patients who
`present with visceral metastases.
`
`OBSTRUCTION AND PERFORATION
`The definitions of both obstruction and
`perforation are either imprecise or not
`
`stated. Much of the literature either as-
`sumes that the reader knows what an ob-
`struction is or does not indicate whether
`obstruction is complete (i.e., total ab-
`sence of flatus or bowel movements for at
`least a day) or partial. Similarly, the type
`of perforation (e.g, free into the peritoneal
`cavity or contained, occurring through the
`cancer or proximal to a complete obstruc-
`tion) is often not well described. The inci-
`dence of complete obstruction appears to
`range between two and 16 percent of new-
`ly diagnosed cases of colorectal can-
`cer.20,26,36 The location of the primary can-
`cer may affect the probability of developing
`a complete obstruction. Levien et al37
`found that carcinomas of the splenic flex-
`ure were more likely to obstruct than were
`carcinomas at other sites. In contrast, ob-
`struction from rectal cancers appears to be
`uncommon.38 Fielding et al39 suggest that
`the proportion of patients with obstruction
`follows the incidence of cancer at each site,
`whereas other reports suggest that the left
`colon36 or the ascending colon38 is the most
`frequent site of obstruction.
`The importance of bowel obstruction
`is supported by its function as an indepen-
`dent covariate in a multivariate analysis of
`outcome, even with stage included in the
`analysis. Crucitti et al40 studied 361 pa-
`tients with colonic or rectal cancer and
`found that the presence of obstruction
`was a significant predictor of death from
`cancer even when stage was included in
`the analysis (obstructed patients had a 31
`percent five-year survival compared with
`a 72 percent survival for patients who
`were not obstructed). Similar findings
`have been reported by others.29,36,41,42
`Wolmark et al42 suggested that the devel-
`opment of obstruction added to the poorer
`prognosis of right-sided colonic cancer,
`but there was no difference in outcome
`between right-sided and left-sided colonic
`cancers in the Gastrointestinal Tumor
`Study Group colonic adjuvant therapy tri-
`als, although in that study the presence of
`obstruction increased the risk of death
`from cancer 1.4-fold. Perforation occurs
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`less commonly. Approximately three-
`quarters of patients operated upon emer-
`gently had obstructions, whereas one-
`quarter had perforations.43 Among the
`patients with perforations, only one-quar-
`ter of perforations were in the prestenotic
`bowel or the dilated cecum; most were
`through the tumor. Of the perforations,
`half were free perforations into the ab-
`dominal cavity, and the remainder were
`perforations into either an abscess cavity
`or a phlegmon. Interestingly, five percent
`of patients had perforations on more than
`one occasion. Perforation appears to be
`associated with local recurrence of dis-
`ease, most likely because malignant cells
`are dispersed throughout the area of in-
`fection.28,41 Perforation increases the risk
`of death from cancer 3.4-fold.28 These dif-
`ferent patterns of presentation change the
`distribution of pain and must be taken
`into account by the clinician.
`
`ROLE OF INFLAMMATORY BOWEL
`DISEASE
`Inflammatory bowel disease is a prema-
`lignant lesion that causes a predisposition
`to colorectal carcinoma when the disease
`enters a chronic, active phase.44 The
`propensity with which carcinoma devel-
`ops may be associated with the degree of
`dysplasia caused by the inflammatory pro-
`cess.45-47 Although chronic ulcerative coli-
`tis has long been associated with an in-
`creased risk for the development of
`invasive carcinoma, recent studies have
`shown that chronic Crohn’s disease is also
`associated with the subsequent develop-
`ment of cancer.48 As a result, among the
`symptomatic patients it is important to
`remember that inflammatory bowel dis-
`ease may lead to bowel cancer. The cu-
`mulative incidence of colorectal cancer in
`inflammatory bowel disease is estimated
`to be five to 10 percent at 20 years and 12
`to 20 percent at 30 years.48 This reinforces
`the need for surveillance in patients with
`inflammatory bowel disease to ensure
`early diagnosis.
`
`Current Status of Diagnosis in the
`Asymptomatic Patient
`BIOLOGY OF FAMILIAL AND SPORADIC
`COLORECTAL CARCINOMA
`The pioneering work of Muto, Bussey,
`and Morson49 revealed that the majority
`of colorectal carcinomas develop from an
`adenomatous polyp. This polyp-to-carci-
`noma sequence is based on several de-
`scriptive but supportive findings: adeno-
`matous polyps have a distribution of
`location similar to that of cancers that
`arise in the large bowel49,50 but appear an
`average of five years earlier than does
`large bowel cancer,49,51 many large bowel
`cancers display remnants of the polyp ad-
`jacent to the primary cancer, serial biopsy
`of polyps that have not been resected re-
`veals a slow process of transformation to
`an invasive cancer,49,52 endoscopic re-
`moval of adenomatous polyps decreases
`the risk of developing bowel cancer by 76
`to 90 percent,6 and natural history studies
`of small polyps left in the colon reveal that
`some polyps less than 0.5 cm in diameter
`may regress whereas others either remain
`unchanged or slowly progress to a larger
`more dysplastic phenotype.53 Cannon-Al-
`bright et al54 have estimated that 19 per-
`cent of the general population forms ade-
`nomatous polyps and, therefore, is at risk
`to develop colorectal carcinoma.
`Three recent findings have markedly
`advanced our understanding of the rela-
`tionship between the formation of adeno-
`matous polyps and invasive carcinomas.
`First, the lesion that precedes the devel-
`opment of a polyp is an aberrant crypt fo-
`cus (ACF) that becomes a microadeno-
`ma. The ACF begins as an outpouching
`of an epithelium-lined sac from the side
`of the crypt of Lieberkuhn that expands
`and eventually develops into a separate
`broad-mouthed crypt.55 Microadenomas
`are identified by methylene blue dye
`staining at colonoscopy or in the patholo-
`gy specimen because their crypt openings
`to the lumen of the bowel are several
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`times larger than the normal crypt open-
`ing.56 Roncucci56 has reported that mi-
`croadenomas may be dysplastic, whereas
`others57,58 have shown that loss of tumor
`suppressor genes and activation of proto-
`oncogenes may occur with frequencies
`similar to these events in polypoid adeno-
`mas. ACF and microadenomas are impor-
`tant because these lesions develop into
`adenomas and carcinomas in animal mod-
`els of carcinogenesis.59 However, the evi-
`dence that ACFs develop into adenoma-
`tous polyps is circumstantial: patients with
`familial adenomatous polyposis (FAP)
`have more ACFs than do patients with
`sporadic colorectal carcinomas, who have
`more ACFs than do controls without can-
`cer.60 Thus, ACF may be an important in-
`termediate marker to aid in the diagnosis
`of patients with colorectal cancer.
`The second finding is that not all
`adenomas are exophytic; they may be flat
`and difficult to detect on colonoscopy.
`The Japanese have focused on the flat
`adenoma61-64 as a precursor lesion to car-
`cinoma; many flat adenomas are ulcerat-
`ed lesions that may be more aggressive
`than exophytic cancers.65 These lesions
`have also been appreciated in European
`patients.66 Further, flat adenomas may be
`precursors to the cancers that develop in
`hereditary nonpolyposis colorectal can-
`cer (HNPCC) because they display the
`microsatellite instability that is observed
`in HNPCC and have a proximal large
`bowel distribution.64 Lynch and his asso-
`ciates have identified several kindreds of
`patients who display the hereditary flat
`adenoma syndrome (HFAS) in which
`colon cancers develop at a later age than
`in FAP patients, have a proximal colon
`distribution, and arise in association with
`flat adenomas.67 However, genetic link-
`age studies suggest that these kindreds
`are linked to deletions on chromosome
`5q and may be variants of FAP rather
`than altered presentations of HNPCC,
`which has prompted the use of the term
`attenuated familial adenomatous polypo-
`sis (AFAP) for this syndrome.68
`
`The third observation is that a frac-
`tion of bowel cancers appear to arise
`without an antecedent polyp. Several re-
`ports have suggested that adenocarcino-
`mas of the bowel may arise without poly-
`poid remnants or altered adjacent
`mucosa.69,70 Bedenne et al71 demonstrat-
`ed that ulcerated, infiltrating cancers in
`the right colon were least likely to be as-
`sociated with an adenomatous polyp.
`These and other results suggested to
`Jass72 that 10 to 30 percent of colorectal
`cancers may not develop from an an-
`tecedent adenomatous polyp but arise de
`novo from mucosa that appears other-
`wise normal or has microadenomas. This
`is important because the current technol-
`ogy for diagnosis in asymptomatic indi-
`viduals requires that a polyp be removed
`in order to prevent bowel cancer. As a re-
`sult, under the present screening guide-
`lines somewhere between 70 and 90 per-
`cent of large bowel cancers may be
`identified and removed before they be-
`come frankly invasive. However, under
`the best of circumstances 10 to 30 percent
`of large bowel cancers may not develop
`from a benign polyp and, as a result, may
`not be detectable or treatable until the le-
`sion is frankly invasive.
`
`MOLECULAR PATHWAYS FOR SPORADIC
`AND INHERITED COLORECTAL
`CARCINOMAS: IMPORTANCE FOR
`DIAGNOSIS
`Current evidence indicates that colorec-
`tal carcinoma develops through as many
`as three related but slightly different mol-
`ecular pathways. The first and best de-
`scribed molecular pathway involves mu-
`tation in a gene called the adenomatous
`polyposis coli (APC) gene. This mutation
`causes the appearance of hundreds to
`thousands of adenomatous polyps in the
`large bowel and is the cause of the auto-
`somally dominantly inherited FAP and
`related syndromes.73 The molecular alter-
`ations that occur in this pathway largely
`involve deletions of alleles of tumor sup-
`
`Vol. 47 No. 2 March/april 1997
`
`77
`
` 15424863, 1997, 2, Downloaded from https://acsjournals.onlinelibrary.wiley.com/doi/10.3322/canjclin.47.2.70, Wiley Online Library on [29/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
`
`Geneoscopy Exhibit 1056, Page 8
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`

`D i a g n o s i n g c o l o r e c t a l c a n c e r
`
`Activation c-Ki-ras
`Activation c-src
`
`Proliferation
`LOH APC
`LOH MCC
`
`LOH P53
`LOH DCC
`
`Normal
`Mucosa
`
`l
`
`ll
`
`lll
`
`Carcinoma
`
`Metastasis
`
`Adenomas
`
`Fig. 1. Genetic alterations in the familial adenomatous polyposis (FAP) type of neoplastic transfor-
`mation of bowel epitheilum. Activation generally implies a mutational event, although it may merely
`be an increase in the expression of a normal gene product or the dephosphorylation of a peptide
`such as c-src. APC = adenomatous polyposis coli gene; DCC = deleted in colorectal cancer
`gene; LOH = loss of heterozygosity. (Reproduced with permission from Jessup et al.76)
`
`Mutation
`hMSH2, hMLH1
`hPMS1, hPMS2
`
`Activation c-Ki-ras
`
`Proliferation ?
`Mutation APC
`
`Mutation P53
`
`Normal
`Mucosa
`
`l
`
`ll
`
`lll
`
`Carcinoma
`
`Metastasis
`
`Adenomas
`
`Fig. 2. Genetic alterations in the hereditary nonpolyposis colorectal carcinoma (HNPCC) type of
`neoplastic transformation of bowel epithelium. Unlike the events in Fig. 1, mutation without loss of
`heterozygosity occurs in the adenomatous polyposis coli (APC) gene, p53, and c-Ki-rasin this
`pathway. The passage through the various classes of adenomas may be shortened.(Reproduced
`with permission from Jessup et al.76)
`
`pressor genes, that is, loss of heterozygos-
`ity (LOH) in APC, p53, and the deleted
`in colorectal cancer (DCC) gene74 com-
`bined with mutational activation of pro-
`to-oncogenes, especially c-Ki-ras (Fig. 1;
`see also reviews in the literature75,76 ). In
`
`contrast, mutation of the human homo-
`logues of the bacterial mutHLS complex
`(hMSH2, hMLH1, hPMS1, and hPMS2)
`produces the DNA mismatch repair
`defects that appear to be the cause of
`HNPCC.77-82 The mutations in DNA mis-
`
`78
`
`Ca—A cancer Journal for Clinicians
`
` 15424863, 1997, 2, Downloaded from https://acsjournals.onlinelibrary.wiley.com/doi/10.3322/canjclin.47.2.70, Wiley Online Library on [29/12/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
`
`Geneoscopy Exhibit 1056, Page 9
`
`

`

`C A C a n c e r J C l i n 1 9 9 7 ; 4 7 : 7 0 - 9 2
`
`match repair enzymes lead to genetic in-
`stability that is reflected in errors in accu-
`rate replication of the repetitive di-, tri-,
`and tetranucleotide repeats that are scat-
`tered throughout the genome.83-86 As a re-
`sult, the genomic instability identified in
`HNPCC is commonly referred to as ei-
`ther replication error positive (RER+) or,
`because microsatellite regions in the
`genome contain the nucleotide repeats,
`as microsatellite instability (MIN). Al-
`though these replication errors produce
`mutations in many of the same tumor
`suppressor genes and proto-oncogenes
`that are affected in the FAP pathway,
`there is a significantly lower frequency of
`LOH in the HNPCC pathway85 (Fig. 2).
`Finally, although many sporadic car-
`cinomas appear to follow either the FAP
`(with mutation and LOH of APC, p53,
`and DCC) or the HNPCC (with RER+
`phenotype and mutation of APC, p53,
`and DCC without LOH) pathway, col-
`orectal carcinomas that arise de novo
`seem to have a slightly different pattern
`of molec