Role of prophylactic colectomy in Lynch syndrome

Lynch Syndrome-Impact of the Type of Deficient Mismatch Repair Gene Mutation on Diagnosis, Clinical Presentation, Surveillance and Therapeutic Approaches

In today's world, with its continuing advancements in genetics, the identification of Lynch syndrome (LS) increasingly relies on sophisticated genetic testing techniques. Most guidelines recommend a tailored surveillance program, as well as personalized prophylactic and therapeutic approaches, according to the type of dMMR gene mutation. Carriers of path_MLH1 and path_MSH2 genes have a higher risk of developing colorectal cancer (CRC), despite intensive colonoscopic surveillance. Conversely, carriers of path_MSH6 and path_PMS2 genes have a lower risk of developing CRC, which may be due to their lower penetrance and later age of onset. Thus, carriers of path_MLH1 or path_MSH2 would theoretically derive greater benefits from total colectomy, compared to low-risk carriers (path_MSH6 and path_PMS2), in which colonoscopic surveillance might achieve an efficient prophylaxis. Furthermore, regarding the risk of endometrial/ovarian cancer development, there is a global agreement to offer both hysterectomy and bilateral salpingo-oophorectomy to path_MLH1, path_MSH2 and path_MSH6 carriers after the age of 40. In patients with CRC, preoperative knowledge of the diagnosis of LS is of tremendous importance, due to the high risk of metachronous CRC. However, this risk depends on the type of dMMR gene mutation. For carriers of the high-risk variants (MLH1, MSH2 and EPCAM) who have already developed colon cancer, it is strongly recommended a subtotal or total colectomy is performed, while partial colectomy followed by endoscopic surveillance is an appropriate management approach to treat colon cancer in carriers of the low-risk variants (MSH6 and PMS2). On the other hand, extended surgery for index rectal cancer (such as total proctocolectomy) is less effective than extended surgery for index colon cancer from the point of view of metachronous CRC risk reduction, and is associated with a decreased quality of life.

Incidences of colorectal adenomas and cancers under colonoscopy surveillance suggest an accelerated "Big Bang" pathway to CRC in three of the four Lynch syndromes

BACKGROUND

Colorectal cancers (CRCs) in the Lynch syndromes have been assumed to emerge through an accelerated adenoma-carcinoma pathway. In this model adenomas with deficient mismatch repair have an increased probability of acquiring additional cancer driver mutation(s) resulting in more rapid progression to malignancy. If this model was accurate, the success of colonoscopy in preventing CRC would be a function of the intervals between colonoscopies and mean sojourn time of detectable adenomas. Contrary to expectations, colonoscopy did not decrease incidence of CRC in the Lynch syndromes and shorter colonoscopy intervals have not been effective in reducing CRC incidence. The prospective Lynch Syndrome Database (PLSD) was designed to examine these issues in carriers of pathogenic variants of the mis-match repair (path_MMR) genes.

MATERIALS AND METHODS

We examined the CRC and colorectal adenoma incidences in 3,574 path_MLH1, path_MSH2, path_MSH6 and path_PMS2 carriers subjected to regular colonoscopy with polypectomy, and considered the results based on sojourn times and stochastic probability paradigms.

RESULTS

Most of the path_MMR carriers in each genetic group had no adenomas. There was no association between incidences of CRC and the presence of adenomas. There was no CRC observed in path_PMS2 carriers.

CONCLUSIONS

Colonoscopy prevented CRC in path_PMS2 carriers but not in the others. Our findings are consistent with colonoscopy surveillance blocking the adenoma-carcinoma pathway by removing identified adenomas which might otherwise become CRCs. However, in the other carriers most CRCs likely arised from dMMR cells in the crypts that have an increased mutation rate with increased stochastic chaotic probabilities for mutations. Therefore, this mechanism, that may be associated with no or only a short sojourn time of MSI tumours as adenomas, could explain the findings in our previous and current reports.

Polygenic background modifies penetrance of monogenic variants for tier 1 genomic conditions

Genetic variation can predispose to disease both through (i) monogenic risk variants that disrupt a physiologic pathway with large effect on disease and (ii) polygenic risk that involves many variants of small effect in different pathways. Few studies have explored the interplay between monogenic and polygenic risk. Here, we study 80,928 individuals to examine whether polygenic background can modify penetrance of disease in tier 1 genomic conditions — familial hypercholesterolemia, hereditary breast and ovarian cancer, and Lynch syndrome. Among carriers of a monogenic risk variant, we estimate substantial gradients in disease risk based on polygenic background — the probability of disease by age 75 years ranged from 17% to 78% for coronary artery disease, 13% to 76% for breast cancer, and 11% to 80% for colon cancer. We propose that accounting for polygenic background is likely to increase accuracy of risk estimation for individuals who inherit a monogenic risk variant.

Genetic variation predisposes to disease via monogenic and polygenic risk variants. Here, the authors assess the interplay between these types of variation on disease penetrance in 80,928 individuals. In carriers of monogenic variants, they show that disease risk is a gradient influenced by polygenic background.

Phenotypic and genotypic heterogeneity of Lynch syndrome: a complex diagnostic challenge

Lynch syndrome is the hereditary disorder that most frequently predisposes to colorectal cancer as well as predisposing to a number of extracolonic cancers, most prominently endometrial cancer. It is caused by germline mutations in the mismatch repair genes. Both its phenotype and genotype show marked heterogeneity. This review gives a historical overview of the syndrome, its heterogeneity, its genomic landscape, and its implications for complex diagnosis, genetic counseling and putative implications for immunotherapy.

Segmental vs extended colectomy in the management of hereditary nonpolyposis colorectal cancer: a systematic review and meta-analysis

AIM

The optimal surgical approach to the management of colorectal cancer in the setting of hereditary nonpolyposis colorectal cancer (HNPCC) is contentious. While some advocate total colectomy, others perform segmental resection followed by regular endoscopic surveillance. This systematic review evaluates the evidence for segmental colectomy (SC) and total (extended) colectomy (TC) in the management of HNPCC.

METHOD

Two major databases (PubMed and Cochrane) were searched using predefined terms. All original articles, published in English, comparing the oncological outcomes of SC and TC in HNPCC patients from January 1950 to July 2013 were included.

RESULTS

Eighty-four studies were identified. After applying exclusion criteria, six studies involving 948 patients were included (mean age 47.4 years, 51.8% male). SC was more commonly performed than TC (n = 780; 82.3%). Mean follow-up was 106.5 months. Metachronous high-risk adenomas were detected more often after SC, although the difference was not statistically significant (23.4% vs 9.6%; OR 2.258, P = 0.057). Metachronous cancers occurred more frequently after SC than after TC (23.5% vs 6.8%; OR 3.679, P < 0.005). However, there was no difference in overall survival (90.7% vs 89.8% for SC and TC, respectively; P = 0.085). Only one study reported operative mortality (0% in each group), there was no report of operative morbidity or functional outcome.

CONCLUSION

The optimal surgical approach in the management of HNPCC remains unclear. More adenomas and cancers occur after SC than after TC but there certainly is no evidence to suggest that more radical surgery leads to improved survival.

Decision Model of Segmental Compared With Total Abdominal Colectomy for Colon Cancer in Hereditary Nonpolyposis Colorectal Cancer

Purpose

In choosing the appropriate surgical option for patients with colon cancer and Lynch syndrome, goals of treatment are to maximize life expectancy while preserving quality of life. This study constructs a decision model that encompasses these two related considerations.

Methods

We constructed a state-transition (Markov) model based on assumptions obtained from available data sources and published literature. Two strategies were considered for the treatment of colon cancer in a patient with Lynch syndrome: segmental colectomy (SEG) and total abdominal colectomy (TAC) with ileorectal anastomosis. Quality-adjusted life years (QALYs) were calculated based on utility states for patients based on the colectomy they received. Multiple sensitivity analyses were planned to examine the impact of each assumption on model results.

Results

For young (30-year-old) patients with Lynch syndrome, mean survival was slightly better with TAC than with SEG (34.8 v 35.5 years). When QALYs were considered, the two strategies were approximately equivalent, with QALYs per patient of 21.5 for SEG and 21.2 for TAC. With advancing age, SEG becomes a more favorable strategy. Results of our model were most sensitive to the utility state of TAC (relative to SEG), rates of metachronous occurrence, and stage of cancer at the time of such occurrence.

Conclusion

SEG and TAC are approximately equivalent strategies for patients with colon cancer and Lynch syndrome. The decision regarding which operation is preferable should be made on the basis of patient factors and preferences, with special emphasis on age and the ability of the patient to utilize intensive surveillance.

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.

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.

Gastric cancer: new genetic developments

Gastric cancer's (GC) incidence shows large geographic differences worldwide with the lowest rates occurring in most Western industrialized countries including the United States and the United Kingdom; in contrast, relatively high rates of GC occur in Japan, Korea, China, and South America, particularly Chile. The Laurén classification system classifies GC under two major histopathological variants: 1) an intestinal type and 2) a diffuse type. The intestinal type is more common in the general population, more likely to be sporadic and related to environmental factors such as diet, particularly salted fish and meat as well as smoked foods, cigarette smoking, and alcohol use. It exhibits components of glandular, solid, or intestinal architecture, as well as tubular structures. On the other hand, the diffuse type is more likely to have a primary genetic etiology, a subset of which, known as hereditary diffuse gastric cancer (HDGC), is due to the E-cadherin (CDH1) germline mutation. The diffuse type pathology is characterized by poorly cohesive clusters of cells which infiltrate the gastric wall, leading to its widespread thickening and rigidity of the gastric wall, known as linitis plastica. Helicobacter pylori infection is associated with risk for both the intestinal and diffuse varieties of gastric cancer. Germline truncating mutations of the CDH1 gene, which codes for the E-cadherin protein, were initially identified in three Maori families from New Zealand that were predisposed to diffuse GC. Since then, similar mutations have been described in more than 40 additional HDGC families of diverse ethnic backgrounds. It is noteworthy that two-thirds of HDGC families reported to date have proved negative for the CDH1 germline mutation. A number of candidate genes have been identified through analysis of the molecular biology of E-cadherin. Patients with evidence of the CDH1 germline mutation in the context of a family history of HDGC must be considered as candidates for prophylactic gastrectomy, given the extreme difficulty in its early diagnosis and its exceedingly poor prognosis when there is regional or distant spread. Specifically, the E-cadherin cytoplasmic tail interacts with catenins, assembling the cell-adhesion complex involved with E-cadherin mediated cell:cell adhesion. Beta-catenin and gamma-catenin compete for the same binding site on the E-cadherin cytoplasmic tail, directly linking the adhesion complex to the cytoskeleton through alpha-catenin. Beta-catenin gene (CTNNB1) mutations have been described predominantly in intestinal-type gastric cancers and CTNNB1 gene amplification and overexpression have recently been described in a mixed-type gastric cancer. This paper reviews the genetics of both intestinal and diffuse types of gastric carcinoma, their differential diagnosis, molecular genetics, pathology, and, when known, their mode of genetic transmission within families.

Lower incidence of colorectal cancer and later age of disease onset in 27 families with pathogenic MSH6 germline mutations compared with families with MLH1 or MSH2 mutations: the German Hereditary Nonpolyposis Colorectal Cancer Consortium

PURPOSE

The aim of the study was the analysis of the involvement and phenotypic manifestations of MSH6 germline mutations in families suspected of hereditary nonpolyposis colorectal cancer (HNPCC).

PATIENTS AND METHODS

Patients were preselected among 706 families by microsatellite instability, immunohistochemistry, and/or exclusion of MLH1 or MSH2 mutations and were subjected to MSH6 mutation analysis. Clinical and molecular data of MSH6 mutation families were compared with data from families with MLH1 and MSH2 mutations.

RESULTS

We identified 27 families with 24 different pathogenic MSH6 germline mutations, representing 3.8% of the total of the families, and 14.7% of all families with DNA mismatch repair (MMR) gene mutations (n = 183). The median age of onset of colorectal cancer in putative mutation carriers was 10 years higher for MSH6 (54 years; 95% CI, 51 to 56) compared with MLH1 and MSH2 (44 years; 95% CI, 43 to 45; log-rank test, P = .0038). Relative to other malignant tumors, colorectal cancer was less frequent in MSH6 families compared with MLH1 and MSH2 families (Fisher's exact test, P < .001). In contrast, the frequency of non-HNPCC-associated tumors was increased (Fisher's exact test, P < .001).

CONCLUSION

Later age of disease onset and lower incidence of colorectal cancer may contribute to a lower proportion of identified MSH6 mutations in families suspected of HNPCC. However, in approximately half of these families, at least one patient developed colorectal or endometrial cancer in the fourth decade of life. Therefore, a surveillance program as stringent as that for families with MLH1 or MSH2 mutations is recommended.