Inherited polyposis syndromes: molecular mechanisms, clinicopathology, and genetic testing

Discovering the Mutational Profile of Early Colorectal Lesions: A Translational Impact

Simple Summary

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Next-generation sequencing technologies have identified new candidate genes and deepened the knowledge of the molecular mechanisms underlying the progression of colonic adenomas towards CRC. The main genetic, epigenetic, and molecular alterations driving the onset and progression of CRC in both hereditary and sporadic settings have also been investigated. The evaluation of the CRC risk based on the molecular characterization of early pre-cancerous lesions may contribute to the development of targeted preventive strategies development, help define specific risk profiles, and identify patients who will benefit from targeted endoscopic surveillance.

Abstract

Colorectal cancer (CRC) develops through a multi-step process characterized by the acquisition of multiple somatic mutations in oncogenes and tumor-suppressor genes, epigenetic alterations and genomic instability. These events lead to the progression from precancerous lesions to advanced carcinomas. This process requires several years in a sporadic setting, while occurring at an early age and or faster in patients affected by hereditary CRC-predisposing syndromes. Since advanced CRC is largely untreatable or unresponsive to standard or targeted therapies, the endoscopic treatment of colonic lesions remains the most efficient CRC-preventive strategy. In this review, we discuss recent studies that have assessed the genetic alterations in early colorectal lesions in both hereditary and sporadic settings. Establishing the genetic profile of early colorectal lesions is a critical goal in the development of risk-based preventive strategies.

Inherited colorectal cancer syndromes

Colorectal cancer is the most common gastrointestinal malignancy and the second leading cause of cancer death in both men and women in the United States. Most colorectal cancer cases diagnosed annually are due to sporadic events, but up to 5% are attributed to known monogenic disorders including Lynch syndrome, familial adenomatous polyposis, MYH-associated polyposis, and the rare hamartomatous polyposis syndromes. These inherited colorectal cancer syndromes confer a markedly increased risk for the development of multiple cancers, and predictive genetic testing is available to identify mutation carriers and at-risk family members. Through personalized strategies for diagnosis and management, a substantial reduction in morbidity and mortality has been appreciated among patients at highest risk for the development of colorectal cancer.

The differential diagnosis and surveillance of hereditary gastrointestinal polyposis syndromes

BACKGROUND

Hereditary gastrointestinal polyposis syndromes account for about 1% of all cases of colorectal cancer and are associated with a broad spectrum of extracolonic tumors. The early detection and accurate classification of these syndromes are essential, since effective methods for surveillance and treatment are available.

METHODS

This review article is based on a selective literature search, the author's own work, and evidence-based guidelines and recommendations.

RESULTS AND CONCLUSIONS

The diagnosis is initially suspected on the basis of the endoscopic findings and polyp histology. Because different syndromes can resemble each other phenotypically, e.g., autosomal dominant familial adenomatous polyposis and autosomal recessive MUTYH-associated polyposis, molecular genetic studies are important for differential diagnosis and for assessing the risk of recurrence. Identification of the familial mutation in an affected patient is a prerequisite for predictive testing in asymptomatic persons at risk and sometimes enables prognostication. In recent years, the rate of detection of mutations has risen by 10% to 30%, and clinically relevant genotype-phenotype correlations have been described for juvenile polyposis syndrome. Except in cases of mild adenomatous polyposis, phenotypic overlap among the hamartomatous polyposes often causes difficulties in differential diagnosis. Thus, in unclear cases, a pathologist with special expertise in gastrointestinal disorders should be consulted for the evaluation of polyp tissue. Aside from the monogenic polyposes, there are many other types of polyposis that are non-hereditary or of unknown cause, including the hyperplastic and mixed polyposis syndromes. Risk-adapted surveillance programs have been established for the more frequently occurring polyposes.

The Italian external quality control program for familial adenomatous polyposis of the colon: five years of experience

Familial adenomatous polyposis is a rare autosomal dominant inherited disease (incidence, 1/8000). More than 90% of families affected by familial adenomatous polyposis have a mutation in the tumor suppressor gene adenomatous polyposis coli (APC). Mutations in this gene are characterized by 100% penetrance, although there is a variation in phenotypic expression of the disease. According to a 2004 survey of the Italian Human Genetic Society, about 264 APC gene molecular genetic tests were performed by Italian laboratories per year. The Italian External Quality Assessment (IEQA), financially supported by the Ministry of Health and coordinated by the Istituto Superiore di Sanità, was started in 2000 to improve the quality of molecular genetic tests in Italy. In the frame of the IEQA, about 50% of public laboratories performing APC gene tests have been monitored. The number of responding public laboratories during the 5 years was 6, 7, 7, 7, and 5 from 2001 to 2006, respectively; on average, 96.3% of samples completely analyzed were correctly genotyped. Methods used by laboratories to detect mutation were direct sequencing, single-strand conformation polymorphism, protein truncation test, and denaturing high-performance liquid chromatography. Written reports were not homogeneous among laboratories, although a new form of written report was proposed to laboratories in 2004. It will be interesting to monitor the effects of the reporting model and the output of this educational action in the future.

Less common colorectal cancer predisposition syndromes

A variety of syndromes confer increased risk for intestinal polyp development, outside the more commonly occurring syndromes. Each of these uncommon syndromes predispose to pathognomonic histologies that are uncommonly observed. Accurate diagnosis of these syndromes is contingent on higher-level pathology review, evaluation of signs and symptoms beyond sole consideration of the polyps, and collection of a detailed family history. When a genetic mutation can be identified in the proband, the management of intestinal and extra-intestinal cancer screening can be more appropriately tailored.

Gastrointestinal illnesses and their effects on the oral cavity

Many disease processes affecting the gastrointestinal (GI) tract may cause observable changes to the oral cavity. In fact, oral cavity changes may represent the first clinical manifestation of an underlying GI condition. Recognition and appropriate referral of a possible GI condition contribute to overall health and wellness in patients. Some of the more important GI conditions that may manifest oral cavity involvement include: reflux disorders, inherited GI polyposis syndromes, and inflammatory bowel disease. This article briefly reviews the aforementioned topics.

Enteroscopy

Until the end of the 20th century, push enteroscopy (PE) was the most commonly used method for the endoscopic investigation of the small bowel. However, PE has been almost completely replaced by double balloon enteroscopy (DBE). Undoubtedly the major endoscopic breakthrough of the last decade, DBE has contributed to the better diagnosis and understanding of diseases of the small bowel, opening-up this obscure part of the gastrointestinal tract to visualisation. Modern diagnostic and therapeutic DBE allows for a deeper and more thorough evaluation of the small bowel than PE, enabling the detection of more pathological lesions. In addition, DBE has for the first time enabled endoscopists to observe the entire small intestine, and has provided endoscopic interventions such as cauterisation of bleeding lesions, polypectomy, placement of small bowel stents, and foreign-body extraction.

Sonographic diagnosis of intestinal polyps in children

Although colonoscopy is the modality of choice for the diagnosis of intestinal polyps, sonography may be the first diagnostic modality in the evaluation of children with this pathology. Graded compression sonography of the small and large bowel may be useful in diagnosing intestinal polyps. A specific diagnosis is possible in many cases as most polyps have a characteristic appearance. Although sonography is not intended to replace endoscopy in the diagnostic work-up of intestinal polyps, it is important for radiologists to be aware of this appearance as they can be the first in making the diagnosis of intestinal polyps using sonography.

Câncer ano-reto-cólico: aspectos atuais II - câncer colorretal - fatores de riscos e prevenção

O câncer colorretal é curável e passível de prevenção. A chave para o alcance desses objetivos é relativamente simples e pode ser aplicada em escala populacional. Basta, para tanto, que sejamos capazes de conscientizar os médicos, independente da sua área especial de atuação, e proporcionar às pessoas o mais fácil alcance às informações médicas expressas em termos simples sobre a profilaxia e o diagnóstico precoce dessa neoplasia maligna, sobretudo, destacando os fatores protetores e os de riscos, principalmente os que são suscetíveis de ser modificados.

Recently identified colon cancer predispositions: MYH and MSH6 mutations

Single-gene germline mutations conferring a high lifetime risk of colorectal cancer (CRC) account for up to 6% of all CRC cases. The most widely studied monogenic colorectal cancer syndromes include familial adenomatous polyposis (FAP) and Lynch syndrome. However, additional syndromes continue to be defined and new predisposition genes are continuing to be identified. Most recently, MYH-associated polyposis (MAP) and an "atypical Lynch syndrome" related to the presence of MSH6 mutations have been linked to an increased risk of CRC. In this review, we summarize basic information related to these newly recognized gene mutations, including the accumulating data on the prevalence and penetrance of deleterious mutations, as well as the management options for identified carriers and their families. Recognizing these heritable syndromes is essential and predictive genetic testing will continue to transform the field of cancer risk assessment by offering the opportunity to focus on more precise risk management and cancer prevention.

Hamartomatous polyposis syndromes

The hamartomatous polyposis syndromes are a heterogeneous group of disorders that share an autosomal-dominant pattern of inheritance and are characterized by hamartomatous polyps of the gastrointestinal tract. These syndromes include juvenile polyposis syndrome, Peutz-Jeghers syndrome and the PTEN hamartoma tumor syndrome. The frequency and location of the polyps vary considerably among syndromes, as does the affected patient's predisposition to the development of gastrointestinal and other malignancies. Although the syndromes are uncommon, it is important for the clinician to recognize these disorders because they are associated with considerable morbidity and mortality, not only from malignancy but also from nonmalignant manifestations such as bleeding, intussusception, and bowel obstruction. Each hamartomatous polyposis syndrome has its own distinctive organ-specific manifestations and each requires a different surveillance strategy, which makes accurate diagnosis crucial for appropriate patient management. The availability of clinical genetic testing for these disorders means that appropriate recognition allows for timely referral for cancer genetic counseling, and often allows for predicative testing in at-risk family members. Promisingly, an understanding of the molecular pathogenesis of these disorders offers insights into the mechanisms underlying the development of sporadic malignancy, and enables rational selection of targeted therapies that warrant further investigation.

Endoscopic resection of nonadenomatous ampullary neoplasms

The safety and effectiveness of endoscopic management of ampullary adenomas is well known. However, data on the endoscopic treatment and long-term outcome of nonadenomatous ampullary neoplasms are lacking. We describe our experience with the endoscopic management and the follow-up of 4 patients with nonadenomatous ampullary neoplasms viz, ampullary carcinoid, gangliocytic paraganglioma, ampullary hamartoma in patients with Peutz-Jegher syndrome and Cowdens syndrome.

Genetic testing in colorectal cancer: who, when, how and why

Colorectal cancer (CRC) is among the most prevalent and preventable forms of cancer worldwide, accounting for over 600,000 deaths in 2005. Both genetic and environmental factors contribute to cancer etiology and estimates suggest that at least one third of CRC has a familial component. There is increased awareness of a strong genetic component to CRC risk, with the identification of several high penetrance alleles that predict increased CRC susceptibility. These include familial adenomatous polyposis (FAP), linked to mutations or deletions of the APC tumor suppressor gene, as well as Lynch syndrome (formerly known as hereditary non-polyposis colorectal cancer or HNPCC), which is linked to mutations or deletions of one or more mismatch repair genes including MLH1, MSH2 and MSH6. In addition, mutations in genes encoding key signaling molecules have been linked to autosomal dominant hamartomatous syndromes that are associated with increased susceptibility to CRC. These include Peutz-Jeghers syndrome, which is linked to mutations in STK11/LKB and Juvenile polyposis, which is linked to mutations in the genes encoding SMAD4 and BMPR1A. In addition to these high penetrance autosomal dominant alleles, recessive mutations in the MYH mismatch repair gene are associated with a phenotype similar to FAP. With the widespread availability of genetic testing for these alleles, physicians will be faced with a complex array of choices in terms of advocating who should be tested, when should such testing take place, how it should be conducted and interpreted and why it changes the management and outcomes for the patient and his or her family.