Colorectal cancer in inflammatory bowel disease: molecular and clinical features Sreekant Murthy, PhD * , Anne Flanigan, PhD, Harris Clearfield, MD Division of Gastroenterolgy and Hepatology, MCP Hahnemann University, Mail Stop 444, Suite 2105 NCB, 245 N 15th Street, Philadelphia, PA 19102-1192, USA The two forms of inflammatory bowel disease (IBD), Crohn’s disease and ulcerative colitis (UC), are characterized by chronic and relapsing inflamma- tion of the intestines. Initiating events, though unclear, presumably occur well before patients are symptomatic. Evidence gathered over the past decade from both IBD patients and animal models of intestinal inflammation have confirmed that IBD represents complex heterogenic forms of diseases, influenced by a combination of environmental, genetic, and immunologic factors working in con- cert [1] to produce exaggerated immune responses, resulting in chronic and re- mitting inflammation. There is familial occurrence of IBD and concordance of disease in mono- zygotic twins. There is a large degree of heterogeneity due to the polygenic nature of the diseases. Chromosome 16 has been specifically linked to Crohn’s disease in non-Jewish families (IBD-1). Overall susceptibility to IBD in certain loci of chromosomes 12, 7, and 3 has been clearly established, in decreasing order [2]. Certain HLA regions on chromosome 2 and 6 are linked to UC [2]. Abnormal mucosal barrier function, aberrant penetration, and recognition of intestinal bacterial and dietary byproducts as foreign antigens cause hyperstimu- lation of the mucosal immune system. This dysregulated immune function involves overactivation of TH1 (Crohn’s disease) and TH2 (UC) helper T-cell responses, resulting in the excessive production of proinflammatory cytokines, causing an imbalance with anti-inflammatory cytokines [3]. In the lamina propria, there is excessive infiltration of neutrophils, macrophages, and T lymphocytes, leading to an increased production of arachidonic acid metabolites, oxidative 0889-8588/03/$ – see front matter D 2003, Elsevier Science (USA). All rights reserved. doi:10.1016/S0889-8588(03)00016-9 Reprinted with permission from Gastroenterology Clinics of North America 2002;31(2):551 – 64. * Corresponding author. E-mail address: [email protected] (S. Murthy). Hematol Oncol Clin N Am 17 (2003) 525 – 537
Transcript
Colorectal cancer in inflammatory bowel
disease: molecular and clinical features
Sreekant Murthy, PhD*, Anne Flanigan, PhD,Harris Clearfield, MD
Division of Gastroenterolgy and Hepatology, MCP Hahnemann University, Mail Stop 444,
Suite 2105 NCB, 245 N 15th Street, Philadelphia, PA 19102-1192, USA
The two forms of inflammatory bowel disease (IBD), Crohn’s disease and
ulcerative colitis (UC), are characterized by chronic and relapsing inflamma-
tion of the intestines. Initiating events, though unclear, presumably occur well
before patients are symptomatic. Evidence gathered over the past decade from
both IBD patients and animal models of intestinal inflammation have confirmed
that IBD represents complex heterogenic forms of diseases, influenced by a
combination of environmental, genetic, and immunologic factors working in con-
cert [1] to produce exaggerated immune responses, resulting in chronic and re-
mitting inflammation.
There is familial occurrence of IBD and concordance of disease in mono-
zygotic twins. There is a large degree of heterogeneity due to the polygenic
nature of the diseases. Chromosome 16 has been specifically linked to Crohn’s
disease in non-Jewish families (IBD-1). Overall susceptibility to IBD in certain
loci of chromosomes 12, 7, and 3 has been clearly established, in decreasing
order [2]. Certain HLA regions on chromosome 2 and 6 are linked to UC [2].
Abnormal mucosal barrier function, aberrant penetration, and recognition of
intestinal bacterial and dietary byproducts as foreign antigens cause hyperstimu-
lation of the mucosal immune system. This dysregulated immune function
involves overactivation of TH1 (Crohn’s disease) and TH2 (UC) helper T-cell
responses, resulting in the excessive production of proinflammatory cytokines,
causing an imbalance with anti-inflammatory cytokines [3]. In the lamina propria,
there is excessive infiltration of neutrophils, macrophages, and T lymphocytes,
leading to an increased production of arachidonic acid metabolites, oxidative
0889-8588/03/$ – see front matter D 2003, Elsevier Science (USA). All rights reserved.
doi:10.1016/S0889-8588(03)00016-9
Reprinted with permission from Gastroenterology Clinics of North America 2002;31(2):551–64.
inflammation and cancer. This observation is important because massive infiltra-
tion and activation of macrophages is commonly observed in IBD.
In SCRC and HCRC, mutation of the APC gene and impairment of its
function are early events [24]. In UC-associated CRC, however, APC gene
mutations are rare. The loss of heterozygosity of APC in both polypoid and flat
lesions in UC cancer patients appear at the same frequency, but is slightly
increased in DALMs in UC [25].
Investigators have studied mutations of the proto-oncogene, Ki-ras, in both
UC-associated CRC and in SCRC [26]. In sporadic cancer, mutations of Ki-ras are
frequently observed. These mutations appear later in the development of CRC
arising from UC. Unfortunately, there have been inconsistencies in the reporting of
Ki-ras mutation frequencies in UC ranging from as low as 3% to as high as 50%
[27]. Carcinomatous lesions and high-grade dysplasia show a generally higher
frequency of Ki-rasmutations [28]. Some studies have recommended screening of
colonic lavages for Ki-ras mutations for the early detection of UC-associated
colon cancer [29], but the validity of this screening remains to be confirmed.
Germ-line mutations of the human MSH2 (a gene whose protein products help
repair mistakes made in DNA replication) and microsatellite D165541 have been
implicated in both HCRC and UC-associated CRC [30,31]. The microsatellite
marker for IBD-1(D16S541) was found in 33% of UC cancer patients, but only
12% of control HCRC. Thirty-two percent of patients with dysplastic UC also
had this genotype, whereas only 8% of patients with nondysplastic UC had the
genotype [31]. The authors of this study [31] suggested that this microsatellite
marker, when combined with other markers, has the potential to be used as a
screening tool for CRC and dysplasia in patients with UC. This recommendation
needs to be confirmed by additional studies.
The roles played by other factors such as TGF-b II receptor, p16, and p27 are
beginning to emerge. Dysregulation of growth factors and cognate receptors may
play an important role in the formation of neoplasms. Recently, a TGF-b 1 type II
receptor (TGF-b 1RII) mutation (via a microsatellite instability) was described in
UC-associated CRC [32]. This study showed that mutations of this gene occur
early in unstable UC neoplasms but are restricted to certain subsets in which there
are microsatellite instabilities at other chromosomal loci. This form of instability
is unrestricted and commonly observed in all unstable SCRCs.
The protein p16 (also known as CDKN2, INK4a, or MTS1), whose loss has
been implicated in cancer, maps to chromosome 9p21 and is an inhibitor for
cyclin-dependent kinase, CDK4, and CDK6. It binds to the phosphorylated
CDK-cyclin complex, resulting in progression from the G1 phase to the S phase
of the cell cycle. Therefore, p16 can negatively regulate the cell cycle and is a
candidate tumor suppressor gene. Loss of p16 is observed in a majority of tumor
cell lines and in most primary tumors. Evidence has shown that transcriptional
silencing as a consequence of hypermethylation is the predominant mechanism of
p16 gene inactivation in SCRC. More recent studies identified the significance of
p16INK4a methylation in the colonic epithelium of patients with long-standing
UC. These results showed that hypermethylation of the p16INK4a promoter
S. Murthy et al / Hematol Oncol Clin N Am 17 (2003) 525–537 529
region is a frequent and early occurring event in UC-associated CRC progres-
sion [33,34].
The protein p27 is yet another CDK inhibitor that negatively regulates the G1
to S phase of the cell cycle. This protein is known to protect against inflam-
mation-induced injury and helps epithelial cell differentiation. Unlike in sporadic
cancer, p27 is underexpressed in CRC that has been associated with UC [35]. The
low expression of this key protein has been suggested to further contribute to the
aggression of cancer in IBD.
b-catenin, a 92-kDa protein, has a high sequence similarity to the polarity gene
Armadillo in Drosophila [36]. This protein plays a key role in signal transduction
and cell adhesion. Altered expression of b-catenin and its binding partners
E-cadherin and the APC protein are frequent early events in SCRC. It appears
that APC is responsible for regulating its homeostatic control; however, with loss
of APC function, b-catenin accumulates in the cytoplasm and nucleus and activates
Tcf4 and c-myc. b-Catenin is normally expressed in the lateral membranes of the
colonic epithelium. It is overexpressed in both sporadic and UC-associated CRC.
This overexpression is closely linked to E-cadherin alterations in UC-associated
CRC. Abnormal b-catenin expression, however, was more closely linked to APC
alterations in sporadic cancers. In sporadic cancers, b-catenin translocates from the
cell membrane to the nucleus or cytoplasm. On the contrary, Karayiannakis et al
[37] have shown that in human UC and Crohn’s disease, b-catenin is always
localized to the cell membrane. Recently, Mikami et al [38] showed stronger
b-catenin staining in UC-associated neoplasms compared with stronger expression
in the nucleus and cytoplasm of sporadic cancers, suggesting different pathways
of tumorigenesis for UC-associated CRC compared with sporadic cancers.
Taken together, some of these diverse molecular events associated with
UC-associated CRC demonstrate a mechanistic connection between inflamma-
tion and tumorigenesis that is distinct from the pathways observed in both HCRC
and SCRC. These findings highlight opportunities to identify distinct molecular
targets to not only determine potential risks of developing cancer but also for
strategizing therapeutic interventions.
Molecular pathways of dysplasia: lessons from animal models
There are many animal models of IBD but only few of these models are ideal
to study the dysplasia–cancer sequence. Certain cotton top tamarins (Sanguinas
oedipus) develop colitis-associated colon cancer in a captive environment,
approximately 3 to 6 times more than those animals without the familial history
of CRC [39]; however, these cancers arise unassociated with dysplasia, which is
different from human UC patients. Other mouse models such as interleukin-B10
knockout and GaI knockout develop colitis-associated adenocarcinoma, but they
have not been adequately used for cancer studies as they relate to humans.
Many investigators have reported the appearance of dysplasia and cancers in
mice, rats, and hamsters when they are fed dextran sulfate sodium solutions. This
S. Murthy et al / Hematol Oncol Clin N Am 17 (2003) 525–537530
model has provided opportunities to evaluate the spectrum of biochemical and
histopathologic changes that migrate from colitis to dysplasia to cancer. In a
recent study, Cooper et al [40] studied the association of clinical disease severity,
incidence, distribution, multifocality of dysplasia, cancer, and immunoexpression
of p53 and b-catenin in a mouse model of dextran sulfate sodium–induced
colitis. The results of the study showed several similarities with human colitis-
associated colon cancer. Similar to humans, only few animals developed
dysplasia/cancer and there was a lack of association between clinical disease
severity and carcinogenesis.
Inflammation scores were higher in those animals with flat cancerous lesions
and invasive cancers, suggesting an association between inflammation and tu-
morigenesis. In contrast to humans, p53 mutations were uncommon in this model.
An interesting observation was the differential overexpression of b-catenin in twotypes of lesions observed in this model. Immunohistochemical studies showed that
DALMs showed complete translocation of membrane b-catenin to the cytoplasm
and nucleus; however, flat lesions exclusively expressed b-catenin on the cell
membrane. This interesting observation suggests different molecular pathways
for different cancerous lesions. Some lesions may have loss of APC function
(DALM) and others may not. Mice expressing a dominant negative N-cadherin
have been shown to develop adenomas [41]. This mutant (NCAD Delta) dem-
onstrated abnormal proliferation, migration, and crypt loss, which eventually
lead to small intestinal adenomas. This unique model could yield an opportunity
to study the role of adhesion molecules and the low risk of small intestinal can-
cers in Crohn’s disease.
In another study, Cooper et al [42] also showed that colitis acts as a promoter
of cancer in mice with multiple intestinal neoplasia, which has a single germ line
mutation of APC. In this model, dextran sulfate sodium-associated colon cancer
occurred though the loss of APC via loss of heterozygosity, as in classic multiple
intestinal neoplasia.
These studies suggest that animal models could serve as valuable tools to
understand the molecular neoplastic pathways of colitis-associated cancer.
Clinical features of cancer in IBD patients
The increase in overall cancer risk in patients with UC results from the
increased incidence of both CRC and hepatobiliary cancer associated with
primary sclerosing cholangitis. An increased risk of CRC is increasingly
recognized in Crohn’s disease as well. Friedman et al [43] screened 259 patients
with Crohn’s colitis every 2 years and concluded that the probability of detecting
dysplasia or carcinoma was 22% by the fourth surveillance. Surveillance
colonoscopy is therefore advised for patients with chronic and extensive Crohn’s
colitis, as well as for CUC. The challenge is to identify risk factors for
malignancy in IBD patients and to develop screening and surveillance strategies
to permit earlier detection and, therefore, more effective therapy.
S. Murthy et al / Hematol Oncol Clin N Am 17 (2003) 525–537 531
Risk factors in IBD patients
Duration and extent of disease
The absolute risk of CRC in UC is 5% to 10% after 20 years of disease and
approximately 30% after 35 years [44]. The risk of CRC is related to the duration
of disease and the extent, with pancolitis patients having a 14.8 relative risk, 2.8
for left-sided colitis, and 1.7 for proctitis [44]. The risk of dysplasia and cancer in
IBD patients is more directly related to the duration and extent of colonic disease
than the age of onset [45,46]. IBD carcinoma occurs at a younger age than in
patients with non-IBD cancer. UC patients have a similar cancer distribution to
those with non-IBD colon malignancies, but patients with Crohn’s disease have a
higher percentage of right-sided lesions, perhaps reflecting the tendency for right-
sided Crohn’s colitis in patients with ileocolitis [47].
Strictures in UC and Crohn’s disease
Dysplasia and cancer are more likely to occur in UC strictures. Gumaste et al
[48] reported a 5% incidence of strictures in their UC patients, but 24% of the
strictures were malignant. Strictures occurring after 20 years of disease were
more likely to be malignant in their study. Strictures occurring in the left colon
and rectum were more often benign. Therefore, those strictures occurring after
20 years of disease, located proximal to the splenic flexure, and presenting with
obstructing symptoms favor malignancy. Although strictures in UC may reveal
no evidence of dysplasia or malignancy by biopsy, several UC stricture cases
were reported that had previously been negative by biopsy but were later found to
have advanced-stage carcinoma, thus raising the question as to whether UC
strictures require colectomy or whether surveillance strategies are appropriate in
such patients [49]. If strictures cannot be adequately evaluated by colonoscopy,
then colectomy should be considered. Strictures in the presence of colonic
Crohn’s disease have been reported to have a 6.8% frequency of malignancy
compared with a 0.7% cancer incidence in similar patients without strictures [50].
Perianal fistulas and malignancy
Rectal carcinoma may present as an acute perianal fistula. One of the authors
(H.C.) encountered a patient who presented in this fashion and the malignant
nature of the fistula was not apparent until a surgical biopsy was performed. In
other instances, the fistulas may be chronic and secondarily develop malignancy.
Carcinoma should be considered when perianal fistulas result in progressive pain,
fail to heal with medical therapy, or rectal stricturing occurs.
Influence of treatment on IBD cancer
The possibility that long-term immunosuppressive therapy such as aza-
thioprine or 6-mercapatopurine could lead to an increased frequency of neo-
S. Murthy et al / Hematol Oncol Clin N Am 17 (2003) 525–537532
plasms is a concern to all who manage patients with IBD. No increased risk of
carcinoma or non-Hodgkin’s lymphoma was found in one series of 775 IBD
patients [51]. Eighty-six patients had been given 2 mg/kg of azathioprine for a
median of 12.5 months. The follow-up was for a median of 9 years. There was no
cancer in either the patients treated with azathioprine or those who did not receive
the therapy; however, many IBD patients are receiving immunosupressive
therapy for considerably longer periods than 1 year, raising the possibility that
the incidence of carcinoma could increase over time. Lymphomas occur with
greater frequency in IBD patients, although the increased incidence appears to be
relatively small. The influence of azathioprine and 6-MP on the development of
lymphoma appears to be little, if any, whereas there is insufficient evidence at
present (because of the relatively short follow-up) to determine whether inflix-
imab promotes malignancies.
Primary sclerosing cholangitis
Marchesa et al [52] compared 27 patients with primary sclerosing cholangitis
with a UC cohort of 1185 patients. Dysplasia during cancer surveillance biopsies
prompted colectomy in 16 patients (59.5%) compared with 11.5% in control
patients. A population-based cohort of 125 primary sclerosing cholangitis
patients from the Swedish Cancer Registry reported a cumulative cancer risk
of 25% after 10 years of UC [53].
Positive family history of sporadic cancer
Patients with UC and Crohn’s disease who have a family history of CRC have
a more than twofold increase in their cancer risk [54]. The risk appears to be
higher if the family member developed cancer prior to age 50 (which would also
increase the cancer risk in non-IBD patients).
Cancer surveillance in UC
Surveillance colonoscopy is predicated on the supposition that detection of
dysplasia will identify those at greatest risk of proceeding to cancer and thus
prompt prophylactic colectomy. The most cost-effective frequency of colonos-
copic surveillance has not been established. There is a consensus that surveil-
lance colonoscopy should be initiated after 8 to 10 years of pancolitis, and started
somewhat later for patients with a history of left-sided colitis. Between 10 and
20 years of disease, the frequency could be every 2 to 3 years but yearly after
20 years of disease. Two biopsies are obtained at 10-cm intervals and placed in
four fixative jars: right, transverse, left, and recto-sigmoid. The procedure should
not be performed during active disease because the regeneration process could
simulate low-grade dysplasia.
Dysplasia is a neoplastic epithelial change without infiltration into the lamina
propria. Many physicians mistakenly believe that dysplasia is a preneoplastic
S. Murthy et al / Hematol Oncol Clin N Am 17 (2003) 525–537 533
disorder, and in one study [55], only 19% correctly defined the term. Further-
more, the designation ‘‘low-grade dysplasia’’ is somewhat unfortunate because it
suggests a benign variant of dysplasia and may thus result in a false sense of
security or inaction as regards colectomy [56]. The average time for progression
of low-grade dysplasia to carcinoma has been reported to be 6.3 years. The
detection of high-grade dysplasia by surveillance colonoscopy not only predicts
future CRC but may also be associated with existing malignancy. Although 69%
of physicians would recommend colectomy for high-grade dysplasia (the
remainder favored continued surveillance), most physicians, unfortunately, would
pursue surveillance for patients with low-grade dysplasia [55]. It is clear that
many physicians do not follow the colectomy recommendations for either low-
grade or high-grade confirmed dysplasia. A diagnosis of low-grade or high-grade
dysplasia should be confirmed by a second pathologist with IBD expertise.
CRC occurs in approximately 40% of patients with a DALM [57]. The finding
of a DALM should prompt colectomy. There has been some question, however,
about the management of patients with chronic UC who are found to have a
colonic adenoma. These lesions could be a subtype of DALM, which may not be
associated with the high predictability for CRC as noted in chronic UC patients.
The distinction between a sporadic adenoma and a DALM is important. If the
lesion lies outside the chronic UC distribution (right sided, for instance, in
patients with left-sided UC) a sporadic adenoma is likely and colectomy need not
be advised. If an adenoma that endoscopically and histologically is compatible
with a sporadic adenoma lies within the distribution of the chronic UC and is
completely removed, multiple biopsies of the ‘‘flat’’ mucosa should be obtained.
If these are negative for dysplasia, surveillance strategies, rather than colectomy,
can be considered [58,59] (Fig. 2).
Fig. 2. Adenoma in the presence of chronic ulcerative colitis. Colectomy should be considered if: (1)
patient is younger than the ‘‘polyp’’ age (less than 40 years of age); (2) polyp cannot be completely
removed or recurs; (3) dysplasia is found in any flat mucosal biopsies; or (4) the patient is not
compliant or a colonoscopy is difficult to perform.
S. Murthy et al / Hematol Oncol Clin N Am 17 (2003) 525–537534
It often is difficult to convince asymptomatic IBD patients about the
importance of surveillance colonoscopies for the early detection of dysplasia or
cancer. Patient education about their potential risks is the most useful motivating
strategy. Perhaps the future availability of more sensitive and reliable predictors
of IBD-associated CRC will permit more specific targeting of patients at risk, and
reduce the frequency of examinations for the remaining patients.
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