Multiple approach to the exploration of genotype-phenotype correlations in familial adenomatous polyposis

Mutational screening of the APC gene in Chilean families with familial adenomatous polyposis: nine novel truncating mutations

PURPOSE

Familial adenomatous polyposis is characterized by the development of hundreds of adenomatous polyps located mainly in the colon and rectum. Patients with familial adenomatous polyposis who do not receive treatment will develop cancer before aged 40 years. This disease is caused by germline mutations in the adenomatous polyposis coli gene. Different studies have shown a correlation between the location of the mutation and the clinical phenotype, such as the grade of severity and/or the presence of extracolonic manifestations, such as desmoid tumors. This study was designed to identify germline mutation in the adenomatous polyposis coli gene in Chilean families with familial adenomatous polyposis.

METHODS

We examined the adenomatous polyposis coli gene in 24 Chilean families with familial adenomatous polyposis. The adenomatous polyposis coli gene was screened for mutations combining single strand conformation polymorphism technique, protein truncation test, and DNA sequencing.

RESULTS

We detected 17 different truncating mutations in 21 of 24 families (87.5 percent); 9 of these were novel. Fourteen mutations were detected in exon 15, being the most frequent c.3,927_3,931delAAAGA, found in 3 of 21 families (14 percent). Eight families (33 percent) showed at least one patient affected with desmoid tumors, presenting mutations between codons 849 and 1,533. Interestingly, two mutations, c.3,632dupA and c.3,783_3,784delTT, leading into a truncating protein at codons 1,216 and 1,274, were associated with almost 100 percent penetrance for desmoid tumors among relatives.

CONCLUSIONS

We achieved 87 percent mutation detection rate in adenomatous polyposis coli gene; more than 50 percent of them were novel. The high percentage of novel mutations found may be because of the genetic composition of the Chilean population, which is an admixture of Amerindian and Spaniards, and the scarce information in the literature about similar populations.

Somatic APC mosaicism: a frequent cause of familial adenomatous polyposis (FAP)

Somatic mutational mosaicism presents a challenge for both molecular and clinical diagnostics and may contribute to deviations from predicted genotype-phenotype correlations. During APC mutation screening in 1,248 unrelated patients with familial adenomatous polyposis (FAP), we identified 75 cases with an assumed or confirmed de novo mutation. Prescreening methods (protein truncation test [PTT], DHPLC) indicated the presence of somatic mosaicism in eight cases (11%). Sequencing of the corresponding fragments revealed very weak mutation signals, pointing to the presence of either nonsense or frameshift mutations at low level. All mutations were confirmed and quantified by SNaPshot analysis: in leukocyte DNA from the eight patients, the percentage of mosaicism varied between 5.5% and 77%, while the proportion of the mutation in DNA extracted from adenomas of the respective patient was consistently higher. The eight mutations identified as mosaic are localized within codons 216-1464 of the APC gene. According to the known genotype-phenotype correlation, patients with mutations in this region exhibit typical or severe FAP. However, six of the eight patients presented with an attenuated or atypical polyposis phenotype. Our data demonstrate that in a fraction of FAP patients the causative APC mutation may not be detected due to weak signals or somatic mosaicism that is restricted to tissues other than blood. SNaPshot analysis was proven to be an easy, rapid, and reliable method of confirming low-level mutations and evaluating the degree of mosaicism. Some of the deviations from the expected phenotype in FAP can be explained by the presence of somatic mosaicism.

Who should be sent for genetic testing in hereditary colorectal cancer syndromes?

Genetic testing is being adopted increasingly to identify individuals with germline mutations that predispose to hereditary colorectal cancer syndromes. Deciding who to test and for which syndrome is of concern to members of the GI oncology community, molecular geneticists, and genetic counselors. The purpose of this review is to help provide guidelines for testing, given that the results influence syndrome diagnosis and clinical management. Although family history may determine whether testing is appropriate and may direct testing to the most informative family member, evolving clinicopathologic features can identify individual patients who warrant testing. Thus, although the usual absence of clinical premonitory signs in hereditary nonpolyposis colorectal cancer (or Lynch syndrome) adds difficulty to its diagnosis, use of the Amsterdam Criteria and Bethesda Guidelines can prove helpful. In contrast, premonitory stigmata such as pigmentations in Peutz-Jeghers syndrome and the phenotypic features of familial adenomatous polyposis aid significantly in syndrome diagnosis. We conclude that the physician's role in advising DNA testing is no small matter, given that a hereditary cancer syndrome's sequelae may be far reaching. Genetic counselors may be extremely helpful to the practicing gastroenterologist, oncologist, or surgeon; when more specialized knowledge is called for, referral can be made to a medical geneticist and/or a medical genetics clinic.

The surgeon's role in cancer prevention. The model in colorectal carcinoma

Cancer Prevention is an emerging field, capturing the old traditional concept of anticipating the development of a major disease and preventing its full impact by early detection, treatment, or aborting the tumorigenic process by a "molecular vaccine" and alleviating the full impact of the disease. Surgeons are important clinician scientists who can carry this discipline forward and develop its full potential in the clinics and in the community. Advances in molecular biology, genetics, and other technologies have permitted seminal understanding of the carcinogenic pathways and identification of targets and intermediate end points in neoplasia. In this review, we will see that we have the means of preventing significant numbers of colorectal carcinomas (CRC).

The Role of Prophylactic Surgery in Cancer Prevention

BACKGROUND

Since the human genome has been sequenced many mysteries of cell biology have been unravelled, thereby clarifying the pathogenesis of several diseases, particularly cancer. In members of kindreds with certain hereditary diseases, it is now possible early in life to predict with great certainty whether or not a family member has inherited the mutated allele causing the disease. In hereditary malignancies this has been particularly important, because in affected family members there is the possibility of removing the organ destined to develop cancer before malignancy develops or while it is in situ. At first consideration, it would appear that "prophylactic surgery" would have a place in many hereditary malignancies; however, the procedure has applicability only if certain criteria are met: (1) the genetic mutation causing the hereditary malignancy must have a very high penetrance and be expressed regardless of environmental factors; (2) there must be a highly reliable test to identify patients who have inherited the mutated gene; (3) the organ must be removed with minimal morbidity and virtually no mortality; (4) there must be a suitable replacement for the function of the removed organ; and (5) there must be a reliable method of determining over time that the patient has been cured by "prophylactic surgery."

CONCLUSIONS

In this monograph we review several hereditary malignancies and consider those where prophylactic surgery might be useful. As we learn, there are various barriers to performing the procedure in many common hereditary cancer syndromes. The archetype disease syndromes, which meet each of the five criteria mentioned above and where prophylactic surgery is most useful, are the type 2 multiple endocrine neoplasia (MEN) syndromes: MEN2A, MEN2B, and the related familial medullary thyroid carcinoma. An additional benefit of the Human Genome Project, has been the development of pharmacologic and biologic compounds that block the metabolic pathway(s) activated by specific genetic mutations. Many of these compounds have shown efficacy in patients with locally advanced or metastatic cancers, and there is the likelihood that they will prove beneficial in preventing the outgrowth of malignant cells in patients destined to develop a hereditary cancer.

Correlations between mutation site in APC and phenotype of familial adenomatous polyposis (FAP): A review of the literature

Mutations in the adenomatous polyposis coli (APC) gene cause familial adenomatous polyposis (FAP). Disease severity and the presence of extracolonic manifestations seem to be correlated with the location of the mutation on the APC gene. In this review, large studies describing genotype-phenotype correlations in FAP were evaluated and categorized. Attenuated FAP (AFAP, <100 colorectal adenomas) is correlated with mutations before codon 157, after codon 1595 and in the alternatively spliced region of exon 9. Severe polyposis (>1000 adenomas) is found in patients with mutations between codons 1250 and 1464. Mutations in the remainder of the APC gene cause an intermediate phenotype (hundred to thousands of adenomas). Congenital hypertrophy of the retinal pigment epithelium (CHRPE) and desmoid tumours are associated with mutations between codons 311 and 1444 and after codon 1444, respectively. No consistent correlations were found for upper gastrointestinal tumours. Genotype-phenotype correlations in FAP will be useful in decisions concerning screening and surgical management of FAP.

[Familial adenomatous polyposis]

Familial adenomatous polyposis is a rare genetic disease characterized by the development of more than a hundred adenomatous polyps in the colorectal area, as well as by extracolonic manifestations. Without treatment, this inherited disease, usually transmitted by autosomal dominant inheritance, predisposes to colorectal cancer. Treatment must be preceded by counseling about the nature of the syndrome and by recommendations for the optimal management and surveillance of the disease. Currently, prophylactic surgical therapy is imperative. However, the type of surgical technique used depends mainly on the severity of the polyposis phenotype, the age of the patient at diagnosis, and a series of special clinical circumstances. Lifetime follow-up of all patients is required. This article reviews the main studies published on familial adenomatous polyposis in order to provide an update on the most appropriate management of these patients.

Balance between endoscopic and genetic information in the choice of ileorectal anastomosis for familial adenomatous polyposis

BACKGROUND AND OBJECTIVES

The number of rectal polyps and the site of mutations in the APC (Adenomatous polyposis coli) gene have been used to guide the surgical management in patients with familial adenomatous polyposis (FAP). The aim of this study is to assess the utility of the APC mutation screening compared to the degree of the rectal polyposis in surgical decision making.

METHODS

The post-surgical courses of 25 patients submitted to subtotal colectomy with ileorectal anastomosis (IRA) were reviewed. Preservation of the rectum was prospectively decided on the basis of well-defined endoscopic criteria. The number of rectal polyps was assessed preoperatively and every 6-12 months. APC gene was screened for mutations by heteroduplex analysis, single strand conformation polymorphism, in vitro synthesized protein (IVSP), and DNA sequencing. Patients negative for APC mutations were tested for MYH mutations.

RESULTS

On the basis of preoperative polyp rectal count we categorized patients as follows: Group I, 5 or fewer adenomas; Group II, 6-9 adenomas; Group III, 10 or more adenomas. After a follow-up ranging from 12 to 225 months we have observed a significant difference of recurrent rectal adenomas between Groups I-II versus III. No difference was detected among patients of Group I and II. The mean number of adenomas/year/patient was 0.67, 1.62, and 9.29 for Group I, II, and III, respectively. Carpeting polyposis of the rectal stump developed in three patients with APC mutation at codon 1309 and two of them needed later proctectomy. Diffuse rectal polyposis was observed in one patient with mutation at exon 9 who had 10 small polyps at time of surgery. Mutation at the 5'-end of APC (codons 144-232), mutation of MYH and unknown APC or MYH mutation were correlated with a low number of polyps both at presentation and follow-up. No IRA patients developed rectal cancer.

CONCLUSIONS

In our experience fewer than 10 rectal polyps at presentation can predict a favorable outcome after IRA. Identification of specific germ-line APC or MYH mutation can address the choice of surgical treatment.

ASCO/SSO review of current role of risk-reducing surgery in common hereditary cancer syndromes

BACKGROUND

A significant portion of cancers are accounted for by a heritable component, which has increasingly been linked to mutations in specific genes. Clinical interventions have been formulated for mutation carriers within affected families. The primary interventions for mutation carriers of highly penetrant syndromes are surgical.

METHODS

The American Society of Clinical Oncology and the Society of Surgical Oncology formed a task force charged with presenting an educational symposium on surgical management of hereditary cancer syndromes at annual society meetings, and this resulted in a position paper on this topic. The content of both the symposium and the position paper was developed as a consensus statement.

RESULTS

This article addresses hereditary breast, colorectal, ovarian/endometrial, and multiple endocrine neoplasias. A brief introduction on the genetics and natural history of each disease is provided, followed by detailed descriptions of modern surgical approaches, clinical and genetic indications, timing of prophylactic surgery, and the efficacy of surgery (when known). Although several recent reviews have addressed the role of genetic testing for cancer susceptibility, this article focuses on the issues surrounding surgical technique, timing, and indications for surgical prophylaxis.

CONCLUSIONS

Risk-reducing surgical treatment of hereditary cancer is a complex undertaking. It requires a clear understanding of the natural history of the disease, realistic appreciation of the potential benefits and risks of these procedures in potentially otherwise healthy individuals, and the long-term sequelae of such interventions, as well as the individual patient's and family's perceptions of surgical risk and anticipated benefit.

Current ideas in desmoid tumours

Desmoid tumours are rare neoplasms of fibroblastic origin which arise with disproportionate frequency in patients with familial adenomatous polyposis (FAP). They are thought to develop in about 10-25% of FAP patients and may be the leading cause of death amongst those who have undergone colectomy. Risk factors include trauma, having a distal germline APC mutation, having a family history of desmoids, and probably oestrogens. In very high-risk individuals there may be a case for delay of colectomy or chemoprophylaxis at the time of surgery. Desmoids are now known to be true neoplasms but with normal telomere length and telomerase activity. FAP-associated tumours seem to carry biallelic APC mutations, one of which lies in the distal part of the gene. Such loss of wild-type APC seems to occur relatively late in tumour development. It is likely that beta-catenin plays an important role in tumourigenesis. FAP-associated desmoids tend to arise in the abdomen or abdominal wall. CT scanning gives the best information on tumour anatomy whilst T2-weighted MRI indicates likely behaviour. Treatment may simply consist of observation. Otherwise, usual first-line therapy is with sulindac with or without an anti-oestrogen. Cytotoxic chemotherapy is an option in unresectable tumours. Surgery is a reasonable first-line treatment in abdominal wall tumours but is risky for intra-abdominal tumours and may necessitate massive small bowel resection. Desmoids are the greatest remaining challenge in the management of FAP and further research into their aetiology needs to be combined with multicentre clinical trials of new treatments in order to improve management of the disease.

Restorative proctocolectomy and ileal pouch-anal anastomosis for familial adenomatous polyposis revisited

Since restorative proctocolectomy (RPC) with ileal-pouch anal anastomosis (IPAA) removes the entire diseased mucosa, it has become firmly established as the standard operative procedure of choice for familial adenomatous polyposis (FAP). Many technical controversies still persist, such as mesenteric lengthening techniques, close rectal wall proctectomy, endoanal mucosectomy vs. double stapled anastomosis, loop ileostomy omission and a laparoscopic approach. Despite the complexity of the operation, IPAA is safe (mortality: 0.5-1%), it carries an acceptable risk of non-life-threatening complications (10-25%), and it achieves good long-term functional outcome with excellent patient satisfaction (over 95%). In contrast to the high incidence in patients operated for ulcerative colitis (UC) (15-20%), the occurrence of pouchitis after IPAA seems to be rare in FAP patients (0-11%). Even after IPAA, FAP patients are still at risk of developing adenomas (and occasional adenocarcinomas), either in the anal canal (10-31%) or in the ileal pouch itself (8-62%), thus requiring lifelong endoscopic monitoring. IPAA operation does not jeopardise pregnancy and childbirth, but it does impair female fecundity and has a low risk of impairment of erection and ejaculation in young males. The latter can almost completely be avoided by a careful "close rectal wall" proctectomy technique. Some argue that low risk patients (e.g. <5 rectal polyps) can be identified where ileorectal anastomosis (IRA) might be reasonable. We feel that the risk of rectal cancer after IRA means that IPAA should be recommended for the vast majority of FAP patients. We accept that in some very selected cases, based on clinical and genetics data (and perhaps influenced by patient choice regarding female fecundity), a stepwise surgical strategy with a primary IPA followed at a later age by a secondary proctectomy with IPAA could be proposed.

An association between the 4G polymorphism in the PAI-1 promoter and the development of aggressive fibromatosis (desmoid tumor) in familial adenomatous polyposis patients

Aggressive fibromatosis is a mesenchymal neoplasm associated with mutations resulting in beta-catenin mediated transcriptional activation. Plasminogen activator inhibitor-1 (PAI-1) is expressed at a high level in aggressive fibromatosis, and using transgenic mice, we found that PAI-1 plays an important role in aggressive fibromatosis tumor formation. Familial adenomatous polyposis is associated with Adenomatous Polyposis Coli gene mutations resulting in beta-catenin mediated transcriptional activation, yet only some patients develop aggressive fibromatosis. Since PAI-1 expression is influenced by a promoter 4G/5G polymorphism, we investigated the incidence of this polymorphism in familial adenomatous polyposis patients who did and who did not develop aggressive fibromatosis, as well as sporadic aggressive fibromatosis patients. There was a trend towards association of the 4G allele (associated with high PAI-1 expression) with the development of aggressive fibromatosis in familial adenomatous polyposis patients (50% vs. 19%, P = 0.1). In familial adenomatous polyposis patients who did not develop aggressive fibromatosis, there was a significantly lower proportion of patients with a 4G allele compared to the healthy control (19% vs. 51%, P = 0.0286). The lower incidence of 4G polymorphism in the PAI-1 promoter may be preventive against the development of aggressive fibromatosis. This data provides additional evidence supporting an important role for PAI-1 in the pathogenesis of aggressive fibromatosis.

ASCO/SSO review of current role of risk-reducing surgery in common hereditary cancer syndromes

Although the etiology of solid cancers is multifactorial, with environmental and genetic factors playing a variable role, a significant portion of the burden of cancer is accounted for by a heritable component. Increasingly, the heritable component of cancer predispositions has been linked to mutations in specific genes, and clinical interventions have been formulated for mutation carriers within affected families. The primary interventions for mutations carriers for highly penetrant syndromes such as multiple endocrine neoplasias, familial adenomatous polyposis, hereditary nonpolyposis colon cancer, and hereditary breast and ovarian cancer syndromes are primarily surgical. For that reason, the American Society of Clinical Oncology (ASCO) and the Society of Surgical Oncology (SSO) have undertaken an educational effort within the oncology community. A joint ASCO/SSO Task Force was charged with presenting an educational symposium on the surgical management of hereditary cancer syndromes at the annual ASCO and SSO meetings, resulting in an educational position article on this topic. Both the content of the symposium and the article were developed as a consensus statement by the Task Force, with the intent of summarizing the current standard of care. This article is divided into four sections addressing breast, colorectal, ovarian and endometrial cancers, and multiple endocrine neoplasia. For each, a brief introduction on the genetics and natural history of the disease is provided, followed by a detailed description of modern surgical approaches, including a description of the clinical and genetic indications and timing of prophylactic surgery, and the efficacy of prophylactic surgery when known. Although a number of recent reviews have addressed the role of genetic testing for cancer susceptibility, including the richly illustrated Cancer Genetics and Cancer Predisposition Testing curriculum by the ASCO Cancer Genetics Working Group (available through http://www.asco.org), this article focuses on the issues surrounding the why, how, and when of surgical prophylaxis for inherited forms of cancer. This is a complex process, which requires a clear understanding of the natural history of the disease and variance of penetrance, a realistic appreciation of the potential benefit and risk of a risk-reducing procedure in a potentially otherwise healthy individual, the long-term sequelae of such surgical intervention, as well as the individual patient and family's perception of surgical risk and anticipated benefit.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal-dominant colorectal cancer syndrome, caused by a germline mutation in the adenomatous polyposis coli (APC) gene, on chromosome 5q21. It is characterized by hundreds of adenomatous colorectal polyps, with an almost inevitable progression to colorectal cancer at an average age of 35 to 40 yr. Associated features include upper gastrointestinal tract polyps, congenital hypertrophy of the retinal pigment epithelium, desmoid tumors, and other extracolonic malignancies. Gardner syndrome is more of a historical subdivision of FAP, characterized by osteomas, dental anomalies, epidermal cysts, and soft tissue tumors. Other specified variants include Turcot syndrome (associated with central nervous system malignancies) and hereditary desmoid disease. Several genotype-phenotype correlations have been observed. Attenuated FAP is a phenotypically distinct entity, presenting with fewer than 100 adenomas. Multiple colorectal adenomas can also be caused by mutations in the human MutY homologue (MYH) gene, in an autosomal recessive condition referred to as MYH associated polyposis (MAP). Endoscopic screening of FAP probands and relatives is advocated as early as the ages of 10-12 yr, with the objective of reducing the occurrence of colorectal cancer. Colectomy remains the optimal prophylactic treatment, while the choice of procedure (subtotal vs proctocolectomy) is still controversial. Along with identifying better chemopreventive agents, optimizing screening of extracolonic cancers and applying new radiological and endoscopic technology to the diagnosis and management of extracolonic features are the major challenges for the future.

Desmoid tumors and current status of management

Desmoid tumors, also known as aggressive fibromatosis, are rare fibroblastic tumors that exhibit a wide range of local aggressiveness, from largely indolent to locally destructive. Understanding of the pathogenesis and the great heterogeneity in the natural history of desmoid tumors is invaluable to the development of therapeutic strategies. The optimal treatment protocol has not yet been established and, in many cases, a multidisciplinary approach including surgery, chemotherapy, and radiation therapy has been employed. The rarity of cases in even major tumor centers has traditionally limited the ability to study this disease. Several novel pharmacologic and biologic treatment approaches are actively being developed, although long-term follow-up is needed for their substantiation.

Surgical Implications of Colorectal Cancer Genetics

The applications of genetics in colorectal cancer are not limited to identifying germ-line mutations in genetically predisposed individuals. Reports on the use of molecular genetic markers as prognostic factors and for assessing the response to therapy are common in the literature. As the primary caregiver in the majority of these cases, the surgeon needs a basic knowledge of colorectal genetics and their implications to the patient and the patient's family. This article discusses a practical approach for some of the issues likely to be encountered by the surgeon.

Familial adenomatous polyposis and mental retardation caused by a de novo chromosomal deletion at 5q15-q22: report of a case

Familial adenomatous polyposis, caused by mutations in the adenomatous polyposis coli gene located at chromosome 5q21, is an autosomal dominant syndrome characterized by polyposis of the colon and rectum and nearly 100 percent progression to colorectal cancer. We report a case of familial adenomatous polyposis and mental retardation caused by a chromosomal deletion at 5q15-q22. Chromosomal analysis is considered part of the evaluation of children with mental retardation and developmental delay. The resulting karyotypes from high-resolution chromosomal analysis can help characterize large deletions, some of which involve known tumor suppressor genes. Because familial adenomatous polyposis may arise from de novo chromosomal deletions involving the adenomatous polyposis coli gene locus, individuals with chromosomal deletions involving 5q21 should be considered at-risk for familial adenomatous polyposis and offered standard screening with flexible sigmoidoscopy by 10 to 12 years of age.

Pediatric aggressive fibromatosis: a retrospective analysis of 13 patients and review of literature

BACKGROUND

Aggressive fibromatosis (AF) is a soft tissue tumor and is rare in childhood, with high potential for local invasiveness and recurrence. General recommendations for the clinical management of pediatric patients with AF remain undetermined.

METHODS

The authors retrospectively analyzed 13 children with AF who were diagnosed from 1987 until 2004 in the Erasmus MC-Sophia Children's Hospital, and a review of the pediatric literature was conducted.

RESULTS

Two patients received preoperative chemotherapy with combined vincristine, actinomycin-D, and cyclophosphamide (VAC). All 13 patients underwent surgery. Three of six patients who underwent incomplete resection received adjuvant treatment, two patients received radiotherapy, and one patient received chemotherapy (VAC). The median follow-up was 3.9 years (range, 0.6-14.0 years). Three patients developed recurrent AF, including two recurrences after patients underwent incomplete resection without adjuvant treatment. Secondary resection was performed, which was incomplete in one patient who subsequently received chemotherapy (VAC). At the time of the current report, all 13 patients were in complete remission. Ten pediatric AF studies, including the current study, with a total of 187 patients were reviewed. Incomplete resection was the most important determinant for disease recurrence; in the authors' opinion, the role of adjuvant therapy needs to be studied further.

CONCLUSIONS

Primary surgery with negative surgical margins was found to be the most successful primary treatment modality for children with AF. Positive margins after surgery indicated a high risk for disease recurrence. Multicenter, prospective (randomized) trials will be necessary to clarify the role of adjuvant treatment for patients with pediatric AF.

A comparison of the phenotype and genotype in adenomatous polyposis patients with and without a family history

OBJECTIVES

Adenomatous polyposis of the colon is often secondary to an inherited mutation in adenomatous polyposis coli (APC) gene, however, approximately one third of patients have no family history of the disease. We studied the phenotype and genotype of adenomatous polyposis in patients without a family history.

METHODS

A cohort of 57 unrelated adenomatous polyposis patients were evaluated. Seventeen patients with no family history were compared with 40 patients who had a positive family history of the disease. Family history and medical records were collected and analyzed. Germline APC and Mut Y homologue (MYH) testing was undertaken.

RESULTS

Patients without a family history were diagnosed with polyposis at an older age (41 years vs. 32 years) and presenting more frequently with symptoms (76 vs 20, P < 0.05). The number of colonic polyps and frequency of extracolonic manifestation associated with adenomatous polyposis did not differ between the two groups. APC mutations were detected less frequently among patients without a family history of the disease (4 out of 17 vs 25 out of 40, P=0.007), even among those with greater than 100 colorectal adenomas (4 out of 12 versus 21 out of 29, P=0.03). One homozygous MYH mutation carrier (G382D) was detected among the six patients without a family history and without a germline APC mutation who were tested.

CONCLUSIONS

Adenomatous polyposis patients without a family history are usually diagnosed with symptoms, and at a later age. Phenotypically, they are similar to those with a family history. However, germline APC mutations are detected far less frequently in patients without a family history. A small percentage of these cases may be secondary to biallelic germline MYH mutations.

Double frameshift mutations in APC and MSH2 in the same individual

Heterozygous germline DNA mismatch repair gene mutations are typically associated with HNPCC. Here we report the case of a proband whose father was known for familial adenomatous polyposis. The number of polyps (less than ten) was not typical of polyposis; therefore, the diagnosis of HNPCC was entertained. Microsatellite instability analyses were performed on peripheral blood and biopsy of a right-sided dysplastic adenoma. The tumour tissue showed high-grade instability, and subsequently, immunohistochemistry showed that neither MSH2 nor MSH6 proteins were expressed in tumour cells. Prophylactic colectomy was performed, and an adenocarcinoma developing within the adenoma was diagnosed (pT1N0). Genomic DNA analysis revealed a novel mutation in MSH2 as a frameshift mutation in exon 7 (c.1,191_1,192dupG). Both parents of the proband were analyzed for MSH2 and APC mutations, and in the father, a truncating mutation in exon 15 of APC was identified as del3471-3473GAGA. This mutation was found to be present in the proband. His mother was found to bear the MSH2 exon 7 mutation. At follow-up, the proband was diagnosed with fundic, antral and duodenal adenomas (one fundic adenoma showed low-grade dysplasia). Several tubular rectal adenomas with low-grade dysplasia were excised. The patient later developed an intra-abdominal desmoid tumour.

Genetic testing for inherited colon cancer

The genes associated with each of the inherited syndromes of colon cancer have now been identified, and genetic testing is available for diagnosis. These syndromes include familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, Peutz-Jeghers syndrome, juvenile polyposis syndrome, and, possibly, Cowden's syndrome. Clinical genetic testing approaches have been developed for each of these syndromes and are now a part of accepted clinical care. Disease-causing mutations can be found in the majority of families affected with one of the inherited syndromes, and, most importantly, once a mutation is found in an index case of the family, relatives can be tested for the presence or absence of that mutation with near 100% accuracy. Cancer screening and management in syndrome families is then based on the results of genetic testing. For the physician to order and properly interpret genetic tests, a basic understanding of the types of mutations that lead to inherited disease and the methods for detecting them is vital. These issues will be presented. Additional clinical issues somewhat unique to genetic testing include genetic counseling and informed consent for genetic testing, both of which will also be reviewed. Often the most difficult aspect of genetic testing is deciding which patients and families should undergo the testing. Furthermore, this issue is quite specific for each of the syndromes. Thus, following presentation of general principles of selection for genetic testing, a detailed approach for identifying persons who should undergo testing for each of the individual syndromes will be given, together with relevant descriptions of the syndromes. Finally, the ongoing work to discover new and possibly more common but less penetrant colon cancer susceptibility genes that cause common familial colon cancer will be presented.

Identification of APC gene mutations in colorectal cancer using universal microarray-based combinatorial sequencing-by-hybridization

Familial adenomatous polyposis (FAP) is an autosomal dominant inherited form of colorectal cancer, caused mostly by mutations in the APC gene. Due to the wide variety of mutations found and the large size of the APC gene, several methods of mutation detection are used, which can be time consuming and costly. Here we demonstrate a new method of mutation detection in the APC gene using an array-based approach termed combinatorial sequencing-by-hybridization (cSBH). In cSBH, a universal probe set is attached to a support and a second one is in solution. Two-probe ligation occurs when a DNA strand from the target PCR product consecutively anneals to both unlabeled array-bound and solution-phase dye-labeled probe, creating all target-complementary long-labeled probes attached to the surface. A standard array reader scores fluorescent signals at each array position. Cell lines and patient DNA with known APC gene mutations were analyzed using a cSBH-based HyChip trade mark product. Results show that this universal hexamer (6-mer) chip can successfully detect a range of mutations. Results are very robust for a continuous readout of 3.6 kb from a PCR target, with 99.97% accuracy on a single HyChip trade mark slide. cSBH is a fast, cost-efficient method for first stage mutation screening in the APC or any other gene.

Hereditary cancer predisposition syndromes

Cancer genetics is increasingly becoming integrated into the practice of modern medical oncology. The ability to distinguish a growing proportion of the 5% to 10% of all cancers that develop in individuals who have inherited a genetic mutation conferring heightened susceptibility to specific cancers may permit targeted efforts in cancer surveillance and prevention. While these individuals comprise a small proportion of the overall burden of cancer, strategies successful in reducing their remarkable cancer risks may be generalizable to the broader population. In this review, we highlight the most common hereditary cancer syndromes, most attributable to genes inherited in an autosomal dominant manner with incomplete penetrance, and a number of rare syndromes in which particular progress has been made. The prevalence, penetrance, tumor spectrum, and underlying genetic defects are discussed and summarized in a large table in which a more comprehensive enumeration of syndromes is provided.

APC genotype is not a prognostic factor in familial adenomatous polyposis patients with colorectal cancer

PURPOSE

Several studies have shown that the clinical phenotype of patients with familial adenomatous polyposis is influenced by the position of the associated germline mutation in the APC gene. The aim of this work was to assess whether the site of the APC mutation may also predict the survival of familial adenomatous polyposis patients with a confirmed diagnosis of colorectal cancer.

METHODS

A total of 387 familial adenomatous polyposis patients with colorectal cancer were examined. Of these, 287 (74 percent) belonged to families with an identified mutation, whereas 100 (26 percent) were from families in which no detectable APC mutation had been found by standard screening methods. The subjects were subdivided into four groups, according to the presence and localization of the identified mutation: with mutation before (a), at (b), or beyond codon 1309 (c), and without identified mutation (d).

RESULTS

The cumulative five-year survival estimate of all cases included in the study was 0.56 (95 percent confidence interval, 0.51-0.61). No difference was observed in survival probability among patients from families with mutations before (0.56; 95 percent confidence interval, 0.49-0.63), at (0.58; 95 percent confidence interval, 0.43-0.72), or beyond (0.52; 95 percent confidence interval, 0.31-0.73) codon 1309 or those from families that were mutation negative (0.58; 95 percent confidence interval, 0.48-0.68) (log-rank test, P = 0.9). Survival analysis did not reveal any significant advantage for patients carrying a mutation in a specific region of the APC gene, after adjustment for age, gender, site, and stage.

CONCLUSION

These data do not support the hypothesis that APC mutation may influence the outcome of familial adenomatous polyposis cases affected by colorectal cancer.

Biomarkers for cancer diagnosis: implications for nutritional research

The biology of disease progression is a complex process that involves multiple sequential steps leading to cellular changes and metabolic events. These molecular events, which may serve as potential biomarkers, can be analyzed by laboratory methods and used to detect a disease such as cancer or indicate the biological exposure to environmental substances including dietary intake. Identification of the genetic, molecular, and clinical events involved in the disease process enables the development of effective therapeutic and preventive measures and the prediction of prognostic outcomes. This article describes various factors that influence nutritional and cancer biomarker research, draws similarities between them, and discusses the measures that have been adapted to validate cancer biomarkers that can potentially be applied to nutritional biomarker research. Nutritional research suffers from a lack of means to quantify relationships between diet and cancer. Biomarkers of dietary intake or metabolism, therefore, could have potential application in study designs for establishing a causal relationship between diet and disease.

Tumor markers and colorectal cancer: utility in management

Colorectal cancer (CRC) is a leading cause of morbidity and mortality. Although genetic testing can screen for rare hereditary CRC syndromes, there is no ideal means of screening for sporadic forms of CRC. This review will focus on markers that are currently used in the management of sporadic CRC and their limitations, as well as possible future clinical applications.

Exclusion of an extracolonic disease modifier locus on chromosome 1p33–36 in a large Swiss familial adenomatous polyposis kindred

Familial adenomatous polyposis (FAP), an autosomal dominantly inherited colorectal cancer predisposition syndrome, displays considerable inter- and intrafamilial phenotypic heterogeneity, which represents a major problem in genetic counselling of APC mutation carriers. The Min mouse model indicated a putative disease modifier locus on chromosome 4, which is syntenic to human chromosome 1p35-36. This finding was subsequently supported by parametric and nonparametric linkage analyses in FAP families, however, without identifying functional variants in candidate genes. Recently, germline mutations in the base-excision repair gene MYH (1p33-34) have been described in patients with multiple adenomas, pointing to a possible role as disease modifier in FAP. Here, we present critical reassessment of one of the largest FAP kindreds published, which was previously used in linkage mapping of 1p35-36. In this family, all affected members harbour the same APC germline mutation (5945delA), but display marked phenotypic variability, in particular regarding the occurrence of extracolonic disease that segregates in several branches of the family tree. Using updated clinical information, additional mutation carriers and polymorphic markers, fine mapping of the critical region as well as mutation analysis of the MYH gene were performed. These investigations allowed us to significantly exclude (i) the 1p33-36 region as a modifier locus and (ii) MYH as a modifier gene for extracolonic disease in this FAP kindred. Our results do not eliminate 1p33-36 from suspicion in other families, but clearly indicate that in our family linkage analysis of further putative candidate regions is necessary to identify a disease modifier locus in FAP.

Genotype and phenotype of patients with both familial adenomatous polyposis and thyroid carcinoma

The incidence of thyroid carcinoma in familial adenomatous polyposis (FAP) is thought to be 1%-2%, with the majority of cases being female. We have investigated the phenotype and genotype of 16 patients with FAP associated thyroid carcinoma. Among 1194 FAP patients studied in two high risk registries in North America (Familial Gastrointestinal Cancer Registry, Toronto and University California, San Francisco), 16 (1.3%) unrelated patients with FAP associated thyroid cancers were identified. Adenomatous polyposis coli (APC) gene testing was performed in 14 of the 16 cases. The average age of diagnosis for FAP and thyroid carcinoma was 29 years (range 17-52 years) and 33 years (range 17-55 years), respectively. All FAP patients except 1 had more than 100 colonic adenomas. Extracolonic manifestations, beside thyroid cancer, were presented in 81% (n = 13) of the patients, including gastric and duodenal polyps, desmoid tumor, osteoma, epidermoid cyst, sebaceous cyst and lipoma. Colorectal cancer was diagnosed in 38% (n = 6) of the patients. The pathology of the FAP associated thyroid cancer was predominantly papillary carcinoma. Germline mutations were identified in 12 of 14 patients tested. Mutations proximal to the mutation cluster region (1286-1513) were detected in 9 cases. Thyroid cancer in our FAP population was rare, predominantly in females and showed papillary carcinoma histology. Additionally, thyroid cancer in our patients occurred in the setting of classic FAP phenotype. Germline mutations were located predominantly outside the APC mutation cluster region.