Evidence Of Mismatch Repair Deficiency Research Articles

Identification, incidence and clinical outcomes of patients (pts) with hypermutated prostate cancer (PC).

5072 Background: A small proportion of metastatic PC exhibit outlier somatic mutation (mut) rates exceeding the average of 4.4 mut/Mb. The incidence, clinical course and treatment response of pts with hypermutation (HM) is poorly characterised. Methods: We performed targeted sequencing from a panel of PC genes using plasma cell-free DNA samples collected from metastatic castration-resistant prostate cancer (mCRPC) pts and calculated somatic mutation burden. HM samples were additionally subjected to whole exome sequencing to determine trinucleotide mutational signatures and microsatellite instability (MSI). Clinical data was retrospectively collected and compared to a control cohort of 199 mCRPC pts. Results: 671 samples from 434 pts had ctDNA > 2% and were evaluable. 32 samples from 24 pts had > 11 mut/Mb and fell above the 95th percentile for mutation burden with a median mutation burden of 34 mut/Mb. 11 pts had deleterious mutations or homozygous deletions in mismatch repair (MMR) genes and 4 further pts had evidence of MMR deficiency (MMRd) from mutational signatures and MSI status. The remaining 9 pts had either BRCA2 mutations (n = 4), Kataegis (localized hypermutation, n = 3), or undefined causes for HM (n = 2). The incidence of MMRd was 3.5% (15/434), and germline MMRd was 0.2% (1/434). For MMRd pts with available clinical data (10/15) at diagnosis, the median age was 73.6 y, 70% had Gleason score ≥8, and 50% presented with M1 disease. Comparing the MMRd with the control cohort, median time from ADT to CRPC was 9.1 m (95% CI 6.9–11.4) vs. 18.2 m (95% CI 15.1–21.3), p = 0.001; median time from CRPC to death was 13.1 m (95% CI 0.3–25.9) vs. 40.1 m (95% CI 32.4–47.8), p < 0.001. Conclusions: HM and MMRd can be identified using liquid biopsy and could help to select pts for immunotherapy.

Evolving approach and clinical significance of detecting DNA mismatch repair deficiency in colorectal carcinoma.

The last two decades have seen significant advancement in our understanding of colorectal tumors with DNA mismatch repair (MMR) deficiency. The ever-emerging revelations of new molecular and genetic alterations in various clinical conditions have necessitated constant refinement of disease terminology and classification. Thus, a case with the clinical condition of hereditary non-polyposis colorectal cancer as defined by the Amsterdam criteria may be one of Lynch syndrome characterized by a germline defect in one of the several MMR genes, one of the yet-to-be-defined "Lynch-like syndrome" if there is evidence of MMR deficiency in the tumor but no detectable germline MMR defect or tumor MLH1 promoter methylation, or "familial colorectal cancer type X" if there is no evidence of MMR deficiency. The detection of these conditions carries significant clinical implications. The detection tools and strategies are constantly evolving. The Bethesda guidelines symbolize a selective approach that uses clinical information and tumor histology as the basis to select high-risk individuals. Such a selective approach has subsequently been found to have limited sensitivity, and is thus gradually giving way to the alternative universal approach that tests all newly diagnosed colorectal cancers. Notably, the universal approach also has its own limitations; its cost-effectiveness in real practice, in particular, remains to be determined. Meanwhile, technological advances such as the next-generation sequencing are offering the promise of direct genetic testing for MMR deficiency at an affordable cost probably in the near future. This article reviews the up-to-date molecular definitions of the various conditions related to MMR deficiency, and discusses the tools and strategies that have been used in detecting these conditions. Special emphasis will be placed on the evolving nature and the clinical importance of the disease definitions and the detection strategies.

Routine screening for mismatch repair proteins: The impact on genetic testing.

525 Background: Lynch Syndrome (LS) accounts for approximately 3% of all colorectal cancers (CRC) and is caused by germline mutations in DNA mismatch repair (MMR) genes. Increasing literature supports routine screening for LS using immunohistochemistry (IHC) to detect loss of MMR protein expression on tumour samples. We evaluated genetic clinic referrals and consequent LS diagnoses at our institution pre and post the adoption of universal screening. Methods: Reflex immunohistochemistry (rIHC) on all colorectal adenocarcinomas was implemented in November 2008. Prior to this IHC was performed at the pathologist’s discretion or upon request. Tumour specimens reviewed from November 2004 to October 2008 (pre rIHC) and from November 2008 to October 2012 (post rIHC) were evaluated and patients with evidence of MMR deficiency (MMR-D) were identified. The number of genetic referrals and number of patients with confirmed LS were determined. Results: During an 8-year period, 1,131 pathology specimens were reviewed in 1,103 patients (Table). Completion of IHC increased from 19% to 75% post implementation of rIHC. Ninety-two percent of incomplete samples in the post rIHC period (133/145) had insufficient tumour material for analysis. In patients with available IHC, 18/96 (20%) in the pre rIHC era were MMR-D of which 44% were referred to genetics, resulting in the diagnosis of LS in 4 patients. In the post rIHC era 30/429 (7%) of patients had evidence of MMR-D of which 20% were referred for genetic testing resulting in the detection of 3 LS patients. Conclusions: Universal testing for MMR protein expression is difficult to achieve, and does not necessarily result in increased genetic testing or Lynch Syndrome diagnosis. Systematic work-up of test results is essential once mismatch repair evaluation is initiated. [Table: see text]

Abstract 32: Lynch syndrome-associated breast cancers: Clinicopathological characteristics of a case series from the Colon CFR

Abstract Background: Lynch Syndrome is an autosomal dominant condition which predisposes to early-onset cancer of the colorectum, endometrium, and to a lesser extent, stomach, ureter and renal pelvis, ovary, brain and small bowel. It is thought, however, that there is no significant increase in risk of developing breast cancer. The aim of this study was to determine the prevalence and clinicopathological features of breast cancers arising in families with a history of both colorectal and breast malignancy. Design: 107 cases of breast carcinoma (BC) from 90 families were identified from the Australasian Colorectal Cancer Family Registry. Comprehensive cancer histories were available for all families: 53 (59%) families met the modified Amsterdam criteria, and the remainder had multiple cancers including at least one early onset (<50 years) colorectal cancer per family. A full histology review of the breast cancers was performed by a single pathologist (MC). DNA was extracted from paraffin-embedded tumors. Tumor sections were stained for the four DNA mismatch repair (MMR) proteins MLH1, PMS2, MSH2 and MSH6. A subset of MLH1 negative tumors was assessed for MLH1 promoter methylation using a MethyLight assay. Microsatellite instability (MSI) testing was performed using a panel of 10 markers and PCR was also performed to detect the somatic V600E BRAF mutation. Results were analysed using 2×2 contingency tables and exact probabilities. Results: Loss of one or more MMR proteins was seen in 18/107 tumors (17%): five cancers showed loss of MLH1 and PMS2, twelve tumors MSH2 and MSH6, and one tumor MSH6 alone. IHC and MSI results were concordant in 85/89 (96%) tumors tested. Invasive MMR-deficient BCs were more likely to be poorly differentiated (p=0.005), steroid hormone receptor negative (p<0.05), have confluent necrosis (p=0.002), have growth in solid sheets (p<0.001) and high mitotic index (p=0.002). Additionally, MMR deficient breast cancers were less likely to have contiguous in situ carcinoma present (p=0.004). No association was seen between MMR status and tumor size, lymphovascular invasion, node status, prominent eosinophilic nucleoli, or tumoral calcification. No somatic BRAF V600E mutation was found. Conclusion: DNA mismatch repair protein deficiency was identified in 18/107 cases (17%) of breast cancer arising in a familial setting of colorectal and breast carcinoma. The MMR-deficient BCs were more likely to be high grade, steroid hormone receptor negative, have areas of solid growth, confluent necrosis and high mitotic index than MMR-proficient tumors. The study suggests that breast cancer arising in a setting of Lynch syndrome commonly demonstrates evidence of MMR deficiency and that breast cancers may represent a valid tissue option for the detection of MMR deficiency where colorectal or other spectrum tumors are difficult to obtain. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 32.

Heritable epigenetic mutation of MLHI in a mother and daughter with Lynch syndrome

Background Lynch syndrome is a hereditary predisposition to colorectal and endometrial cancers, in addition to cancers of the stomach, ovary, upper urinary tract, small bowel, hepatobiliary tract, skin and brain. Lynch syndrome is caused by defects in DNA mismatch repair (MMR), and germline mutations in MLHl, MSH2, MSH6 and PMS2 as well as high levels of tumor microsatellite instability (MSI) and loss of MMR protein expression are frequently found. MMR deficiency due to loss of MLH1 in tumor tissue may also be due to gene silencing resulting from hypermethylation of the MLH1 promoter, which is found in 15% of sporadic colorectal and endometrial cancers, and as the second “hit” in some individuals with germline mutations in MLH1. Recently, epigenetic silencing of MLH1 in normal body cells has been proposed as a novel cause of predisposition to Lynch syndrome associated tumors. Twenty five cases of hypermethylation of the MLH1 promoter in peripheral blood (MLH1 epimutation) of individuals with young onset colorectal cancer and/or endometrial cancer have been reported. The heritability of MLH1 epimutation is still under investigation. Methods and results A 39-year-old woman from the Philippines was diagnosed with stage III rectal cancer. Her rectal biopsy was screened for evidence of MMR deficiency, which showed high levels of MSI and loss of MLH1 and PMS2 protein expression. Her mother was diagnosed with synchronous colon and endometrial cancers at age 40. She underwent germline mutation analysis of MLHl which failed to identify a mutation. Her rectal tumor was screened for MLH1 promoter methylation and BRAF V600E, which showed hypermethylation of the MLH1 promoter in both tumor and normal colonic mucosa, and negative BRAF V600E. Analysis of MLH1 promoter methylation in her peripheral blood was consistent with MLH1 epimutation. Tissue from her mother’s colon tumor, endometrial tumor, and normal body tissue showed high levels of MSI, loss of MLH1 protein expression, negative BRAF V600E, and hypermethylation of the MLH1 promoter. Her mother died from her colon cancer in 1995, thus peripheral blood was not available. The patient has two unaffected siblings, ages 31 and 35, who have undergone MLH1 epimutation testing. Neither showed hypermethylation of the MLH1 promoter in peripheral blood.

Lynch Syndrome and Related Familial Colorectal Cancers

Lynch syndrome (hereditary non-polyposis colorectal cancer, HNPCC) refers to autosomal dominant predisposition to colorectal, endometrial, and a spectrum of other cancers. The syndrome is due to heterozygous germ line mutations in one of the mismatch repair genes MLH1, MSH2, MSH6, and PMS2. Amsterdam I and II criteria for clinical diagnosis and Bethesda guidelines for molecular testing of suspected patients usually point out additional families in which there is no evidence of mismatch repair deficiency even after screening by microsatellite instability analysis and/or immunohistochemistry for mismatch repair proteins. Hence, the term "Lynch syndrome" should be restricted to those families with germ line mutations in one of the mismatch repair genes. Familial colorectal tumors with no evidence of mismatch repair deficiency were shown to be clinically and molecularly distinct from classical Lynch syndrome tumors and, therefore, were designated "familial colorectal cancer type X" (FCC-X). The predisposing gene(s) to FCC-X is as yet unknown, but extensive research is currently underway to delineate its etiology. Given the above distinctions, the term hereditary nonpolyposis colorectal cancer (HNPCC), which was formerly used to refer to clinically diagnosed colorectal cancer families that might or might not have mismatch repair deficiency, is being replaced by one of the more informative names: Lynch syndrome and FCC-X.

New Developments in Lynch Syndrome (Hereditary Nonpolyposis Colorectal Cancer) and Mismatch Repair Gene Testing

New Developments in Lynch Syndrome (Hereditary Nonpolyposis Colorectal Cancer) and Mismatch Repair Gene Testing

Differential Features of Colorectal Cancers Fulfilling Amsterdam Criteria without Involvement of the Mutator Pathway

Hereditary nonpolyposis colorectal cancer (HNPCC) is the commonest form of inherited colorectal cancer. Whereas it has been known that mismatch repair gene mutations are the underlying cause of HNPCC, an undetermined number of patients do not have these alterations. The main objectives of this study were to assess the relevance of clinically defined HNPCC patients without characteristic mutator pathway alterations and to identify their specific features. This was a prospective, population-based, cohort that included 1,309 newly diagnosed colorectal cancer patients. Demographic, clinical, pathologic data and tumor DNA from probands as well as a detailed family history were collected. Microsatellite analysis and MLH1, MSH2, and MSH6 immunohistochemistry were done. Germ line MLH1 and MSH2 mutational analysis was done in all patients with evidence of MMR alterations. Twenty-five patients (1.9%) fulfilled Amsterdam criteria of HNPCC but 15 (60%) of them did not have microsatellite instability and showed normal expression of MMR proteins. These patients presented mostly left-sided tumors without lymphocytic infiltrate; they were older, had fewer family members affected with colorectal or endometrial cancers, and more often fulfilled Amsterdam II criteria than HNPCC patients with microsatellite instability. Like unstable HNPCC patients, this group without mutator pathway alterations had a significant percentage of synchronous and metachronous adenomatous polyps and cancers. We define an important group of HNPCC families with specific features, no evidence of mismatch repair deficiency, and an autosomal dominant trait with a lesser penetrance than HNPCC with deficiency.

Functional Evidence of Mismatch Repair Deficiency in Non-Obstructive Azoospermia

Genomic integrity requires a functional DNA mismatch repair (MMR) pathway. Rodents and humans lacking the MMR proteins MLH1 or MSH2 are prone to tumorigenesis and testicular pathology. The survival response to alkylating agents provides an excellent functional assay to detect MMR abnormalities. We tested the hypothesis that men with idiopathic, primary non-obstructive azoospermia exhibit a high tolerance to alkylating agent exposure, and moderate to high microsatellite instability (MI) with associated abnormalities of MSH2 and MLH1 proteins.