Molecular biology of colorectal cancer and clinical consequences for colorectal cancer syndromes

Because of the accomplishments in biotechnical research in the past few decades our knowledge about the molecular mechanisms of carcinogenesis has grown rapidly. Colorectal cancer has been one of the most intensively investigated tumor entities, and it seems to be well established that colorectal tumor growth is associated with an accumulation of acquired somatic mutational events in tumor suppressor genes and oncogenes. Recent progress in our understanding of the molecular basis of the most prevalent colorectal cancer syndromes, such as hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP), is reflected by modifications in diagnosis and therapy. Identification and characterization of the causative genes for these colorectal cancer syndromes have enabled precise presymptomatic detection of mutations in individuals who bear an a priori risk of about 50% of developing colorectal cancer. Genotype-phenotype correlations might further increase the clinical management of hereditary colorectal cancer. Even though developments in cancer research are restricted to the minority of individuals with hereditary cancer syndromes, growing knowledge about the effect of low penetrance variations in tumor suppressor genes may affect the diagnosis and therapy of sporadic colorectal cancer. Received: 10 December 1997 / Accepted: 18 June 1998     

Predictive molecular diagnosis and preventive surgical treatment of hereditary colorectal carcinoma: a new field of interest for surgical research]

Colorectal cancer is one of the most frequent cancers in the Western hemisphere. It seems to be well established that colorectal tumors develop as a result of an accumulation of inherited and/or acquired somatic mutational events in tumor suppressor genes and oncogenes. An increasing understanding of the molecular basis of the most prevalent colorectal cancer syndromes, such as hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP), is reflected by modifications in diagnosis and therapy. Therefore, strategies have been developed for predictive molecular diagnosis and preventive surgical treatment of colorectal cancer syndromes. In the future surgical research will participate in research and development in the field of molecular diagnosis of colorectal cancer and will then evaluate the clinical management concepts as a result.     

Prophylaktische Chirurgie des Mamma- und Ovarialkarzinoms

New insights into the genetic basis of carcinogenesis have been obtained by modern molecular biological techniques. Several susceptibility genes are known. The hereditary breast and ovarian cancer syndrome (germline mutations in BRCA1 and BRCA2) and endometrial cancer in the context of the hereditary non-polyposis colorectal cancer syndrome (HNPCC), germline mutations in mismatch-repair genes, are the most frequent hereditary cancer syndromes in gynaecology. Mutations in TP53 (Li-Fraumeni syndrome) and PTEN (Cowden's disease), associated with increased risk of breast cancer, are responsible for a smaller portion of familial breast cancer.The risk of inheritance and disease can be identified and defined by investigating family history, risk calculation programs, and genetic testing. Afterwards, options of primary, secondary, and tertiary prevention can be formulated. Presently, prophylactic surgery is the only option proven by clinical trials that can reduce the mortality of hereditary breast and ovarian cancer.     

Microsatellite instability in colorectal cancer

BACKGROUND: Microsatellite instability (MSI) causes hereditary non-polyposis colorectal cancer (HNPCC), and occurs in about 15 per cent of sporadic colorectal cancers. Although the basic mechanisms are not clear, there is increased understanding of the clinicopathological consequences of MSI. METHODS: Medline was searched for articles with a combination of keywords relating to MSI in colorectal cancer, focusing on molecular mechanisms, clinicopathological implications, and prognostic and predictive value. Emphasis was placed on articles from the past 5 years. RESULTS: The genetic mechanisms differ in hereditary (germline mutation) and sporadic (epigenetic silencing) colorectal cancer. The MSI pathway frequently has altered transforming growth factor beta receptor II and BAX genes, often beta-catenin, and occasionally p16INK4A and PTEN. Changes in K-ras, adenomatous polyposis coli and p53 are rare. Polymerase chain reaction testing for MSI is superior to immunohistochemistry, but complicated by the number and types of nucleotide markers. The Bethesda panel guides HNPCC testing, but guidelines are lacking for general screening. The presence and role of low-frequency MSI remains controversial. Tumours with MSI tend to occur in the proximal colon and be large, but they have a good prognosis. Their reduced response to adjuvant chemotherapy requires confirmation. CONCLUSION: Research on colorectal cancer needs to be stratified according to microsatellite status in order further to explore the molecular mechanisms and clinicopathological consequences of MSI.     

Hereditäres kolorektales Karzinom

One of the main challenges in the clinical management of familial colorectal cancer (CRC) remains the overlap of syndromes with different underlying genetic causes and the differentiated risk management of colorectal and associated malignancies. The Lynch syndrome (hereditary non-polyposis colorectal cancer, HNPCC) is characterized by the development of colorectal, endometrial, gastric and other cancers and is caused by a mutation in one of the mismatch repair (MMR) genes. Microsatellite instability (MSI) and/or immunohistochemistry (IHC) are important prognostic factors and may predict the response to chemotherapy. Familial adenomatous polyposis (FAP) may be seen as a counterpart to Lynch syndrome, responsible for <1% of all CRC cases. Recently the MUTYH gene has been identified as a further polyposis gene. The associated disorder has been termed MYH-associated polyposis (MAP) and displays an autosomal recessive pattern of inheritance. For clinical management, distinguishing between Lynch syndrome, attenuated FAP and MAP is important for risk assessment, surveillance recommendations and indication for prophylactic surgery.     

Präventive Chirurgie des vererbten colorectalen Carcinoms als Folge molekularer Diagnostik

Numerous inherited genetic changes predisposing to cancer have already been identified and the number is increasing. Accurate prediction of individual risk by means of molecular diagnosis implies clinical consequences in the treatment of cancer-predisposing syndromes. Using familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC) as an example, we present here the underlying genetic changes that contribute to tumor development. These genetic alterations can be efficiently identified through molecular diagnostic techniques. Identification of the familial germline mutation permits one to distinguish mutation carriers from non-mutation carriers within affected families and results in individually tailored surveillance and prevention. Therefore, molecular diagnosis is making a contribution to the advances in preventive surgical therapy. The indications are discussed.     

Hereditary carcinoma: pathogenesis and diagnosis

Effective prevention of cancer in patients with a hereditary disposition to malignant tumours was made possible by intensive prevention programs and molecular diagnosis. Taken hereditary non-polyposis colorectal cancer (HNPCC) as an example this article deals with the pathogenesis and molecular diagnosis in hereditary dispositions to cancer. HNPCC is inherited in an autosomal-dominant fashion and caused by germline mutations in genes responsible for detection an removal of DNA-basepair-mismatches (DNA-mismatch-repair-genes). The error rate in DNA replication is reduced thousandfold by these genes. A defective DNA-mismatch-repair results in tumours if the increased mutation rate causes alterations of tumour-suppressor- or oncogenes. HNPCC patients develop colorectal cancer but also tumours of the renal pelvis, the ureter, the small bowel, the endometrium and less often in other organs. The clinical presentation of these tumours may be characteristic, the clinical diagnosis may be guided by different clinical criteria catalogues. The suspicion is proven by the identification of a germline mutation in DNA-mismatch-repair-genes. This laborious diagnostic procedure is often preceded by prescreening procedures as the detection of microsatellite instability or immunohistochemical tests. Once the germline mutation is identified in a affected family member, the first degree relatives may be tested for this mutation. If they have inherited the mutation, they harbour a extremely high risk for developing cancer and therefore may be included in prevention programs. This so called predictive testing must be preceded by genetic counseling.     

Molecular genetics improves the management of hereditary non-polyposis colorectal cancer.

BACKGROUND: The syndrome of hereditary non-polyposis colorectal cancer (HNPCC) can be diagnosed fairly accurately using clinical criteria and a family history. Identifying HNPCC helps to prevent large-bowel cancer, or allows cancer to be treated at an early stage. Once the syndrome has been diagnosed a family member's risk can be judged approximately from a family tree, or it can now be predicted accurately if the causative mutation is known. OBJECTIVE: This study involved attempts to improve the management of a family with HNPCC over a period of 10 years. Clinical diagnostic criteria, colonoscopic surveillance, surgical treatment, genetic counselling, molecular genetic research, and finally predictive genetic testing were applied as they evolved during this time. SUBJECTS AND METHODS: A rural general practitioner first noted inherited large-bowel cancer in the family and began screening subjects as they presented, using rigid sigmoidoscopy at the local hospital. At the time that the disorder was recognised as being HNPCC (1987), screening by means of colonoscopy at our university hospital was aimed primarily at first-degree relatives of affected individuals. After realising how many were at risk, screening was brought closer to the family. A team of clinicians and researchers visited the local hospital to identify and counsel those at risk and to perform screening colonoscopy. Family members were recruited for research to find the gene and its mutation that causes the disease, to develop an accurate predictive test and to reduce the number of subjects undergoing surveillance colonoscopies. RESULTS: There are approximately 500 individuals in this family. In the 10 years of this study the number of subjects who have been counselled for increased genetic risk or who have requested colonoscopic surveillance for HNPCC in this kindred has increased from 20 to 140. After the causative mutation was found in the hMLH1 gene on chromosome 3, a test for it has reduced the number of subjects who need screening colonoscopy by over 70%. A protocol has been devised to inform family members, to acquire material for research in order to provide genetic counselling for (pre-test and post-test) risk, and to test for the mutation. Eventually, identifying those with the mutation should focus surveillance accurately. CONCLUSIONS: The benefits of restricting screening to subjects with the mutation that causes colorectal cancer and of performing operations to prevent cancer are hard to measure accurately. However, it is likely that at least half the family members will be able to avoid colonoscopic screening, some deaths from cancer should be prevented, and the cost of preventing and treating cancer in the family should fall substantially.     

Erbliches Coloncarcinom ohne Polyposis (HNPCC) ohne Erfüllung der Amsterdam-Kriterien

Epidemiologic data suggest that an underlying genetic disposition can be detected in up to 10% of all colorectal cancer patients and autosomal dominantly inherited hereditary non-polyposis colorectal cancer (HNPCC) is the entity most frequently identified. It was described first by A. Warthin in 1895 in "Family G" and is characterized by a predisposition to an early onset of colorectal cancer and other intestinal or genitourinary tumors. We report the case of a 61-year-old woman with five different cancers. Although the strict Amsterdam Criteria were not fulfilled, molecular analysis revealed HNPCC; further genetic testing in the family confirmed that the 36-year-old and so far healthy son had inherited the germline mutation of his affected mother. Genetic testing in clinically suspected HNPCC cases is recommended for patients with colorectal cancer meeting the Amsterdam Criteria. In patients meeting one of Bethesda Criteria 2-7 without meeting the Amsterdam Criteria, germline mutation analysis is recommended only in MSI-positive tumors.     

Recognition and treatment of patients with hereditary nonpolyposis colon cancer (Lynch syndromes I and II).

Primary genetic factors are etiologic in at least 5-10% of patients with colon cancer. The polyposis syndromes (FPC) are easily identified examples because of the spectacular number of polyps. The hereditary nonpolyposis syndromes (HNPCC), although five times more common than FPC, are usually not recognized because they do not have such a distinctive clinical, premonitory genetic marker. Colorectal cancer expression was surveyed in 10 extended, thoroughly documented HNPCC kindreds. One hundred sixteen patients were found to have 183 colorectal cancers. Despite the striking family history, less than 5% were correctly treated by subtotal colectomy. This provided a unique opportunity to study the natural history. Five findings differed significantly (p less than 0.05) from patients with sporadic colon cancer: (1) mean age of initial colon cancer diagnosed was 45.6 years; (2) 69.1% of first colon cancers were located proximal to the splenic flexure of the colon; (3) 18.1% had synchronous colon cancer; (4) 24.2% had metachronous colon cancer develop with life table analysis showing the risk for a metachronous lesion at 10 years to be 40%; and (5) only 23.3% of cancers were located in the sigmoid colon or rectum. Based on this data, it is recommended that the family history of all patients with a newly diagnosed colon cancer be evaluated for evidence of this syndrome. If an autosomal dominant inheritance pattern emerges, an in-depth genetic investigation is indicated. When HNPCC is confirmed, the following recommendations apply: a subtotal abdominal colectomy is indicated at the time of the initial colon cancer because of the risk of synchronous and metachronous lesions. The rectum should be spared in favor of careful lifetime surveillance because of the proclivity for proximal colon cancer involvement. As yet unaffected members of a newly diagnosed HNPCC kindred who are in the "direct genetic line" should be cautioned that they are at 50% risk and must begin an intensive surveillance program beginning in the third decade with careful attention to the right colon. Patients from newly diagnosed HNPCC families who have had a previous conventional colectomy for colon cancer should, at the very least, enter an intensive surveillance program; a prophylactic completion subtotal colectomy should be considered for patients who are less than totally compliant.     

Surgery of hereditary colorectal carcinoma

Hereditary colorectal cancer syndromes account for about 7% of all colorectal carcinomas. The most frequent form is Hereditary Nonpolyposis Colorectal Cancer (HNPCC). Identification, cloning and sequence analysis of the predisposing genes enables identification of mutation carriers and non-mutation carriers, respectively. These genetic informations can be used in an individually tailored clinical surveillance program and may ultimately result in standard preventive surgical treatment. In classical FAP the surgical standard is performing a restorative proctocolectomy. It is still unclear now, if this procedure should be modified in attenuated forms (colectomy with ileorectostomy). Due to a high rate of synchronous and metachronous carcinomas a subtotal colectomy in the case of first colon cancer seems to be indicated in HNPCC patients. A proctocolectomy or a restorative proctocolectomy should be weighed in case of carcinomas in the lower rectum. These procedures should be performed under the precondition of identification of the pathogenic germline mutation in the patient, only. In addition, a synchronous prophylactic hysterectomy with oophorectomy should be recommended postmenopausal gene carriers. Intensive counseling of the patient should proceed these preventive procedures involving surgeons, gastroenterologists, geneticists, molecular biologists, gynecologists, physicians and psychologists. It is recommended to have patients treated exclusively in specialized centers. Currently, six interdisciplinary centers for cancer surveillance and early diagnosis in hereditary colorectal cancer are being sponsored in Germany by the Deutsche Krebshilfe since 1999. In the future clinical studies have to be conducted to evaluate the efficacy of extended colorectal resections versus efficacy of surveillance and conventional resections according to general oncological principles.     

遗传性非息肉病性结直肠癌的外科治疗

目的:探讨遗传性非息肉病性结直肠癌(HNPCC)患者行预防性全结肠切除或全结肠直肠切除治疗的合理性.方法:分析近年来连续诊治的12例HNPCC患者结直肠癌常规部分结直肠切除治疗后发生异时原发结直肠癌的风险.结果:HNPCC患者初次结直肠癌常规手术治疗后发生异时原发结直肠癌的10年累积风险达52%,第一次异时结直肠癌常规手术治疗后发生异时原发结直肠癌的5年累积风险达50%.结论:HNPCC患者结直肠癌常规部分结直肠切除治疗后发生异时原发结直肠癌的风险很高,行预防性全结肠切除或全结肠直肠切除治疗具有合理性.     

Family and personal history in colorectal cancer patients: what are we missing?

OBJECTIVE: Family and personal history of colorectal cancer and associated tumours are crucial in identifying families with hereditary nonpolyposis colorectal cancer (HNPCC). The aim of this study was to determine the adequacy of these aspects of history-taking in the management of colorectal cancer patients. PATIENTS AND METHODS: Colorectal cancer patients attending outpatient follow-up were interviewed to obtain a detailed family and personal history of cancers. The medical notes were then reviewed to identify whether these had been documented previously. RESULTS: One hundred and one patients took part. In seven, no family history had been recorded; none of these actually had a significant pedigree. In 88, the family history was not significant, a finding correctly documented in the records. Three had a high-risk family history and another three had a personal history of other possible HNPCC-related cancers. In each of these patients, the relevant findings had been documented, but no further action had been taken. CONCLUSIONS: Family history was taken in the majority of patients, but in the only three with a pedigree indicative of HNPCC, its significance was not appreciated. The potential relevance of multiple HNPCC-related cancers in the same individual was also overlooked. Improved education and referral pathways are needed to ensure that families with HNPCC have access to appropriate surveillance and genetic testing.     

Sporadisches und hereditäres Karzinom von Kolon und Rektum

In recent years, there have been major advances regarding the understanding of the pathogenesis of sporadic and hereditary colorectal cancer on the basis of molecular research. The clinical implications of this knowledge differ for the sporadic and hereditary forms. In sporadic colorectal cancer, gene mutations occur in colorectal cells but not as germline mutations. Even though molecular data currently do not influence the clinical management of this form of colorectal cancer, promising molecular approaches exist for the assessment of prognosis, early detection, prevention, and therapy. Germline mutations are the cause of hereditary colorectal cancers, in which molecular methods have a major impact on diagnosis and therapy. Prophylactic surgery is accepted for patients with familial adenomatous polyposis (FAP), but not for patients with hereditary non-polyposis colorectal cancer (HNPCC), the second main form of hereditary colorectal cancer. Further studies will have to clarity this issue.     

Clinical significance of HNPCC, surgical aspects of early recognition

A hereditary background may be demonstrated in approximately 15-20% of colorectal carcinomas. Familial adenomatous polyposis syndrome (FAP) constitutes about 1% of this patient population whereas hereditary non-polyposis colorectal carcinoma (HNPCC) makes up a further 3-6% of colorectal malignancies. The clinical features of HNPCC are dominant right colon localization, early age of onset, high prevalence of synchronous and metachronous tumors. Germline mutations of the so-called mismatch repair genes can be demonstrated in the genetic background of HNPCC. Screening and careful follow-up of these families are essential since the lifetime occurrence of colorectal carcinomas and HNPCC associated tumors has an 80-85% prevalence. The recognition of the affected families may be accomplished by taking a thorough family history, spanning several generations based on the Amsterdam and Bethesda Criteria, immunohistological investigations of the removed specimens and finally the exact identification of the pathologic MMR gene mutations. Radical surgical intervention is advised in cases of proven mutation carriers who are suffering from CRC. The index persons and their family members must be under regular control for their lifetime, with one-to-two year intervals to prevent fatal disease. The initiation of a national HNPCC register would further decrease the mortality and morbidity of the disease.     

Non-polyposis colorectal cancer in subjects under 55 years of age: frequency and phenotype of hereditary or familial syndromes

Young age is believed to be a risk factor for hereditary or familial non-polyposis colorectal cancer. Present study analysed frequency, phenotype and familial cancer risk of 82 subjects with colorectal cancer under 55 years of age. According to age and family history, probands have been subdivided into 5 groups: Hereditary Non-Polyposis Colorectal Cancer (HNPCC) (8.2% of cases); Suspected HNPCC (7.3%); Non-specific familial aggregation of colorectal cancer (AFACC) (19.5%); Early-onset colorectal cancer (diagnosis under 35 years of age) (CCG) (6.1%); Sporadic colorectal cancer (CCS) (58.5%). Proportions of probands with multiple colonic tumours were highest in HNPCC (57.1%), but present in AFACC (12.5%) and CCG (20.0%) groups, as well. Extracolonic, in particular endometrial and ovarian cancers have been found in HNPCC and AFACC probands. Tumours of proximal colon were most frequent in HNPCC, suspected HNPCC, CCG patients. Eleven-years survival rate was higher in HNPCC probands then in CCS group. Familial cancer risk in HNPCC was 3 times as much as in CCG + CCS groups. Diagnosis of colorectal cancer under 55 years of age is associated with an high frequency of hereditary or familial cases. Genetic tests, surveillance and screening programs in these patients must be based on extensive phenotype and pedigree analyses. HNPCC is widely represented in young colorectal cancer patients and is associated with a high risk of multiple synchronous or metacronous colonic and extracolonic tumours. Total colectomy and eventual hysterectomy with bilateral oophorectomy seem therefore recommendable options in these patients.     

Hereditary colorectal cancer syndromes: familial adenomatous polyposis and lynch syndrome

Familial colorectal cancer (CRC) accounts for 10% to 20% of all cases of CRC. Two major autosomal dominant forms of heritable CRC are familial adenomatous polyposis (FAP) and Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer). Along with the risk for CRC, both syndromes are associated with elevated risk for other tumors. Improved understanding of the genetic basis of these diseases has not only facilitated the identification and screening of at-risk individuals and the development of prophylactic or early-stage intervention strategies but also provided better insight into sporadic CRC. This article reviews the clinical and genetic characteristics of FAP and Lynch syndrome, recommended screening and surveillance practices, and appropriate surgical and nonsurgical interventions.     

Genetic testing for hereditary nonpolyposis colorectal cancer

Approximately 80 per cent of patients with colorectal cancer have sporadic disease whereas the remaining 20 per cent seem to have a genetic component. Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common autosomal dominant hereditary syndrome predisposing to colorectal cancer. Various methods have been described to screen for HNPCC and to directly test for mismatch repair gene mutations. This study evaluates the initial results of 1) microsatellite instability (MSI) and immunohistochemistry (IHC) staining of tumors and 2) genetic sequencing for mismatch repair gene mutations in patients suspected to have HNPCC. Appropriate patients for HNPCC testing were identified through a high-risk colorectal cancer clinic. Of those patients screened only those who met Amsterdam criteria (AC) for HNPCC or were young age onset (YAO) (<40 years of age) were eligible for testing. The tumors underwent testing for MSI and had IHC performed in those patients with available tumor specimens. MSI was performed on the five markers approved by the NIH consensus conference. MSI-High (MSI-H) was defined as two or more markers being unstable. IHC was done with commercially available stains for MLH1 and MSH2. All patients had sequencing of the MLH1 and MSH2 genes performed to search for mutations by a commercial laboratory. Genetic counseling was provided and written informed consent was obtained. Fourteen patients were part of kindreds that met the AC. An additional 10 patients were <40 years of age at diagnosis of colorectal cancer but lacked any family history. Testing for MSI and IHC was performed on those available tissue blocks. Of the AC patients five had MSH2 mutations and two had MLH1 variants. Of the five with MSH2 mutations three of four had MSI-H tumors and all four had loss of expression of MSH2 on IHC. Of the MLH1 variants only one had MSI-H tumor and lacked expression of MLH-1 on IHC. Of those patients with no mutation identified three of six had MSI-H tumors. For those patients YAO no genetic mutations were identified. Two of the seven had MSI-H tumors. Genetic testing for HNPCC even in those patients fulfilling the rigid AC yielded mutations in only five of 14 patients with variants of unknown significance being found in an additional two patients. Only one MSH2 variant of unknown significance was identified in the 10 YAO patients, which would suggest that screening in this group of patients with MSI and/or IHC would be appropriate.     

Familial colorectal cancer: a concept revisited

Objective  The family history of patients with colorectal cancer (CRC) shows an increased risk of disease although evident inherited syndromes are demonstrable in only a small percentage of patients. The purpose of this study was to identify factors that might suggest an inherited component in the transmission of CRC.
Method  The study monitored 880 consecutive patients between 1980 and 2005 treated for CRC.
Results  Familial adenomatous polyposis (FAP) was found in only one patient, and a classical mutation of hereditary nonpolyposis colon cancer was found in only two patients. The risk assessment was possible mainly because of factors such as early onset CRC, the presence of multiple primary tumours and a high risk family history. Considering these 36 more patients were suspected to be high risk and referred for further genetic testing. At least one first-degree relative with CRC was reported in 140 patients. In 49 patients, CRC was diagnosed before 50 years of age. Multiple primary tumours, colonic or extra colonic, synchronous or metachronous were found in 136 patients.
Conclusion  Our study suggests that if only patients with identified mutations are taken into consideration, then the percentage of evident hereditary colon cancer is very low, but this percentage quickly increases if we make marginal adjustments to the identifying criteria. It seems that it is the physician's clinical suspicion, more than the fulfilment of rigid criteria, which plays a fundamental role in the timely identification and a subsequent focused treatment of patients with hereditary CRC.