Clinical Implications of Our Advancing Knowledge of Colorectal Cancer Genetics: Inherited Syndromes, Prognosis, Prevention, Screening and Therapeutics

Familial/inherited cancer syndrome: a focus on the highly consanguineous Arab population

The study of hereditary cancer, which accounts for ~10% of cancer cases worldwide is an important subfield of oncology. Our understanding of hereditary cancers has greatly advanced with recent advances in sequencing technology, but as with any genetic trait, gene frequencies of cancer-associated mutations vary across populations, and most studies that have located hereditary cancer genes have been conducted on European or Asian populations. There is an urgent need to trace hereditary cancer genes across the Arab world. Hereditary disease is particularly prevalent among members of consanguineous populations, and consanguineous marriages are particularly common in the Arab world. There are also cultural and educational idiosyncrasies that differentiate Arab populations from other more thoroughly studied groups with respect to cancer awareness and treatment. Therefore, a review of the literature on hereditary cancers in this understudied population was undertaken. We report that BRCA mutations are not as prevalent among Arab breast cancer patients as they are among other ethnic groups, and therefore, other genes may play a more important role. A wide variety of germline inherited mutations that are associated with cancer are discussed, with particular attention to breast, ovarian, colorectal, prostate, and brain cancers. Finally, we describe the state of the profession of familial cancer genetic counselling in the Arab world, and the clinics and societies dedicated to its advances. We describe the complexities of genetic counselling that are specific to the Arab world. Understanding hereditary cancer is heavily dependent on understanding population-specific variations in cancer-associated gene frequencies.

Hereditary cancer syndromes as model systems for chemopreventive agent development

Research in chemoprevention has undergone a shift in emphasis for pragmatic reasons from large, phase III randomized studies to earlier phase studies focused on safety, mechanisms, and utilization of surrogate endpoints such as biomarkers instead of cancer incidence. This transition permits trials to be conducted in smaller populations and at substantially reduced costs while still yielding valuable information. This article will summarize some of the current chemoprevention challenges and the justification for the use of animal models to facilitate identification and testing of chemopreventive agents as illustrated though four inherited cancer syndromes. Preclinical models of inherited cancer syndromes serve as prototypical systems in which chemopreventive agents can be developed for ultimate application to both the sporadic and inherited cancer settings.

Improved testing for microsatellite instability in colorectal cancer using a simplified 3-marker assay

BACKGROUND

In colorectal cancer (CRC), microsatellite instability (MSI) is a valuable marker of defective DNA mismatch repair that identifies cancers with distinct phenotypic properties, including favorable survival. However, the optimal assay for MSI status is unknown. We have evaluated a simplified 3-marker assay for MSI and compared it with the 5-marker (NCI) assay to see if technical variations in MSI testing are important.

MATERIALS AND METHODS

DNA samples from 357 CRCs were evaluated for MSI using the 5 microsatellite markers recommended for the NCI assay (BAT 25, BAT26, D2S123, D5S346, and D17S250). Results were compared with a simplified 3-marker assay (BAT25, BAT26, and D2S123). CRCs identified as MSI were evaluated for their clinical, pathological, and genetic characteristics.

RESULTS

The 5-marker assay identified 96 cancers as MSI. Only 56 of these were MSI by the 3-marker assay (3-marker+ group), leaving 40 cases identified as MSI only by NCI criteria (3-marker- group). The remaining 261 cancers were microsatellite stable (MSS). The 3-marker+ MSI tumors had features characteristic of MSI tumors: more proximal, poorly differentiated, associated with hereditary nonpolyposis colorectal cancer (HNPCC), more BRAF mutations, fewer KRAS mutations, better 5-year disease-specific survival, more frequent mismatch repair (MMR) protein loss, and less likely to be metastatic on presentation (P < .05). Chromosomal arm loss was observed only in 3-marker- MSI and MSS cancers (P < .05).

CONCLUSION

The 3-marker MSI assay outperforms the traditional 5-marker assay for identifying patients with favorable prognosis and homogeneous clinical and genetic features. More accurate MSI testing should improve prognostic and predictive scoring systems for colorectal cancer.

Parental attitudes, beliefs, and perceptions about genetic testing for FAP and colorectal cancer surveillance in minors

Familial adenomatous polyposis (FAP) is the second most common hereditary colorectal cancer syndrome and confers a nearly 100% lifetime risk of developing colorectal cancer. Understanding factors that facilitate and inhibit genetic testing and cancer surveillance in children who are members of families affected by FAP will better equip clinicians to clarify misunderstandings and facilitate appropriate care. The aims of this study were to examine parental attitudes and beliefs regarding endoscopic surveillance and genetic testing in minors at risk for developing FAP. This cross-sectional study includes analyses of qualitative and quantitative interview data collected from parents of children with or at risk for FAP. This report includes data from 28 parents with a total of 51 biological children between 10-17 years of age. The parents had a clinical and/or genetic diagnosis of FAP. Most commonly reported facilitators included provider recommendation (surveillance) and personalized medical management (genetic testing). Most commonly reported barriers included lack of provider recommendation (surveillance) and cost (genetic testing).

Family history? The forgotten question in high-risk colorectal cancer patients

AIM

The aim of the study was to investigate the frequency and detail of family history recorded for patients diagnosed with potentially high-risk colorectal cancer, and to determine the proportion of these patients referred to a high-risk assessment clinic.

METHOD

Medical records of patients diagnosed with colorectal cancer under the age of 50 admitted to a major Sydney teaching hospital were reviewed. The proportion of records containing information about family history was calculated. Associations between recording of family history and demographic and clinical characteristics of patients were investigated. Logistic regression modelling was performed to identify significant, independent predictors of study outcomes.

RESULTS

Of 113 patients with colorectal cancer diagnosed under the age of 50 years, 61 (54%, 95% CI: 44-63%) had an entry in their hospital medical record about family history. Family history was significantly less likely to be recorded for females, for those admitted via the Emergency Department, and for those with shorter lengths of stay. A significant family history was found in 51% of the 61 patients who had a family history recorded. Records of patients attending specialist colorectal surgeons were significantly more likely to contain information about family history than those who attended other specialists (P = 0.04). Only 14 patients (12%, 95% CI: 7-20%) were formally referred for further genetic assessment.

CONCLUSION

These results suggest that family history is still being neglected in routine clinical practice, and high-risk assessment services are underutilized, implying the need for further dissemination of guidelines with regard to the recognition and management of hereditary colorectal cancer.

Hereditary colorectal cancer syndromes and the role of the surgical oncologist

The expanding understanding of the genetic basis to hereditary colon cancer syndromes is dismantling previously conceived categorizations and shedding light on why those schemes often failed in past. This review highlights evolving concepts regarding the genetic diagnosis and clinical management of the more commonly inherited colorectal cancer syndromes, including a discussion of recently described familial syndromes. This review also addresses clinician responsibilities in recognition of familial syndromes and provision of counseling.

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.

Pathophysiology, clinical presentation, and management of colon cancer

Colon cancer is believed to arise from two types of precursor polyps via two distinct pathways: conventional adenomas by the conventional adenoma-to-carcinoma sequence and serrated adenomas according to the serrated adenoma-to-carcinoma theory. Conventional adenomas arise from mutation of the APC gene; progression to colon cancer is a multistep process. The fundamental genetic defect in serrated adenomas is unknown. Environmental factors can increase the risk for colon cancer. Advanced colon cancer often presents with symptoms, but early colon cancer and premalignant adenomatous polyps commonly are asymptomatic, rendering them difficult to detect and providing the rationale for mass screening of adults over age 50.

Reducing the incidence and mortality of colon cancer: mass screening and colonoscopic polypectomy

Most colon cancers arise from conventional adenomatous polyps (conventional adenoma-to-carcinoma sequence), while some colon cancers appear to arise from the recently recognized serrated adenomatous polyp (serrated adenoma-to-carcinoma theory). Because conventional adenomas and serrated adenomas are usually asymptomatic, mass screening of asymptomatic patients has become the cornerstone for detecting and eliminating these precursor lesions to reduce the risk of colon cancer. Colonoscopy has become the primary screening test because of its high sensitivity and specificity, and the ability to perform polypectomy. Other screening tests include guaiac tests or fecal immunochemical tests (FIT) for fecal occult blood, and flexible sigmoidoscopy. A minimal colonoscopic withdrawal time of 6 minutes is important to maximize polyp detection at colonoscopy. Chromoendoscopy is an experimental technique used to highlight abnormal colonic areas to identify neoplastic tissue and to potentially determine the histology of colonic polyps at colonoscopy based on superficial pit anatomy.