Frequency of mutations in mismatch repair genes in a population-based study of women with ovarian cancer

MSH2 role in BRCA1-driven tumorigenesis: A preliminary study in yeast and in human tumors from BRCA1-VUS carriers

BRCA1 interacts with several proteins implicated in homologous and non homologous recombination and in mismatch repair. The aim of this study is to determine if MSH2, a well known partner of BRCA1 involved in DNA repair, may contribute to breast and ovarian cancer development and progression. To better understand the functional interaction between BRCA1 and MSH2, we studied the effect of the deletion of MSH2 gene on BRCA1-induced genome instability in yeast. Preliminary results in yeast indicated that MSH2 and BRCA1 may interact to modulate homologous recombination (HR). We also carried out a genetic and epigenetic profiling of MSH2 gene by mutational analysis and promoter methylation evaluation in 9 breast and 2 ovarian tumors from carriers of BRCA1 unknown significance variants (VUS). 2/2 ovarian and 2/9 breast tumors carried MSH2 somatic mutations possible pathogenics (4/11, 36%): a missense mutation in exon 3 (p.G162R), a duplication of exon 1 and a deletion of exon 2. In addition, two germline synonymous variants in exon 11 were identified. None of the tumors showed promoter methylation. In conclusion, a surprisingly high frequency of MSH2 gene mutations has been found in tumor tissues from BRCA1 VUS carrier patients. This result supports the indication deriving from the yeast model that BRCA1 driven tumorigenesis may be modulated by MSH2.

A founder MLH1 mutation in Lynch syndrome families from Piedmont, Italy, is associated with an increased risk of pancreatic tumours and diverse immunohistochemical patterns

The MLH1 c.2252_2253delAA mutation was found in 11 unrelated families from a restricted area south-west of Turin among 140 families with mutations in the mismatch repair genes. The mutation is located in the highly conserved C-terminal region, responsible for dimerization with the PMS2 protein. Twenty-five tumour tissues from 61 individuals with the c.2252_2253delAA mutation were tested for microsatellite instability (MSI) and protein expression. We compared the clinical features of these families versus the rest of our cohort and screened for a founder effect. All but one tumours showed the MSI-high mutator phenotype. Normal, focal and lack of MLH1 staining were observed in 16, 36 and 48 % of tumours, respectively. PMS2 expression was always lost. The mutation co-segregated with Lynch syndrome-related cancers in all informative families. All families but one fulfilled Amsterdam criteria, a frequency higher than in other MLH1 mutants. This was even more evident for AC II (72.7 vs. 57.5 %). Moreover, all families had at least one colon cancer diagnosed before 50 years and one case with multiple Lynch syndrome-related tumours. Interestingly, a statistically significant (p = 0.0057) higher frequency of pancreatic tumours was observed compared to families with other MLH1 mutations: 8.2 % of affected individuals versus 1.6 %. Haplotype analysis demonstrated a common ancestral origin of the mutation, which originated about 1,550 years ago. The mutation is currently classified as having an uncertain clinical significance. Clinical features, tissue analysis and co-segregation with disease strongly support the hypothesis that the MLH1 c.2252_2253delAA mutation has a pathogenic effect.

Why have ovarian cancer mortality rates declined? Part III. Prospects for the future

Over the last 40 years, the age-adjusted ovarian cancer mortality rate in the USA declined by 23%. The decline in mortality paralleled a decline in incidence, which was largely due to changes in reproductive risk factors. There was no reduction in ovarian cancer case-fatality at 12 years, indicating that improvements in early detection or in treatment did not contribute to the decline in mortality. Here, we discuss potential strategies to further reduce ovarian cancer mortality through prevention, early detection and treatment. The first approach is to increase genetic testing, in order to identify women who are at a high risk of developing ovarian cancer and offer them preventive bilateral salpingo-oophorectomy. At present, up to 17% of ovarian cancers are potentially preventable through population-based genetic testing of known ovarian cancer susceptibility genes. The second approach is to increase the proportion of ovarian cancer patients who achieve a status of no residual disease through primary debulking surgery and subsequently receive adjuvant intraperitoneal chemotherapy. We believe that through a combination of screening to better identify low-volume advanced stage ovarian cancer, aggressive surgery to leave no residual disease and adjuvant intraperitoneal chemotherapy, the cure rate of ovarian cancer might be improved significantly.

Risk factors for ovarian cancers with and without microsatellite instability

OBJECTIVE

In a population-based sample of epithelial ovarian cancers, the objective of this study was to evaluate the association between microsatellite instability (MSI) status and the following factors: (1) ovarian cancer risk factors and (2) the distribution of the specific histologic subtypes.

PATIENTS AND METHODS

Participants were drawn from 3 population-based studies of primary epithelial ovarian cancer; tumor DNA was analyzed using 5 standardized microsatellite markers to assess the MSI status. Patients were divided into 3 groups (MSI-high, MSI-low, and MSI-stable) according to the National Cancer Institute criteria. We compared the prevalence of specific known risk and protective factors among the 3 subgroups, including body mass index, smoking history, parity, BRCA1 and BRCA2 mutation status, past oral contraceptive use, and tubal ligation. Similarly, we compared the distribution of the histologic subtypes among the 3 subgroups.

RESULTS

A total of 917 ovarian cancer patients were included. One hundred twenty-seven cases of cancer (13.8%) were MSI-high. Subgroup analyses according to smoking, body mass index, parity, past oral contraceptive use, and past tubal ligation did not reveal any statistically significance differences among the groups. Among the 29 patients with BRCA1 mutations, 20.7% had MSI-high cancers compared with 5.9% among 17 patients with BRCA2 mutations. The proportions of different ovarian cancer histologies among the various MSI subgroups were similar.

CONCLUSIONS

The prevalence of risk and protective factors among ovarian cancer patients is similar for cancers with and without MSI. The distributions of MSI do not differ significantly among ovarian cancers with different histologies. Ovarian cancer patients with BRCA1 mutations had a 21% rate of MSI-high tumors compared with 6% among patients with BRCA2 mutations, but this difference was not statistically significant.

Emerging importance of mismatch repair components including UvrD helicase and their cross-talk with the development of drug resistance in malaria parasite

Human malaria is an important parasitic infection responsible for a significant number of deaths worldwide, particularly in tropical and subtropical regions. The recent scenario has worsened mainly because of the emergence of drug-resistant malaria parasites having the potential to spread across the world. Drug-resistant parasites possess a defective mismatch repair (MMR); therefore, it is essential to explore its mechanism in detail to determine the underlying cause. Recently, artemisinin-resistant parasites have been reported to exhibit nonsynonymous single nucleotide polymorphisms in genes involved in MMR pathways such as MutL homolog (MLH) and UvrD. Plasmodium falciparum MLH is an endonuclease required to restore the defective MMR in drug-resistant W2 strain of P. falciparum. Although the role of helicases in eukaryotic MMR has been questioned, the identification and characterization of the UvrD helicase and their cross-talk with MLH in P. falciparum suggests the possible involvement of UvrD in MMR. A comparative genome-wide analysis revealed the presence of the UvrD helicase in Plasmodium species, while it is absent in human host. Therefore, PfUvrD may emerge as a suitable drug target to control malaria. This review study is focused on recent developments in MMR biochemistry, emerging importance of the UvrD helicase, possibility of its involvement in MMR and the emerging cross-talk between MMR components and drug resistance in malaria parasite.

Ovarian cancer

Epithelial ovarian cancer is the commonest cause of gynaecological cancer-associated death. The disease typically presents in postmenopausal women, with a few months of abdominal pain and distension. Most women have advanced disease (International Federation of Gynecology and Obstetrics [FIGO] stage III), for which the standard of care remains surgery and platinum-based cytotoxic chemotherapy. Although this treatment can be curative for most patients with early stage disease, most women with advanced disease will develop many episodes of recurrent disease with progressively shorter disease-free intervals. These episodes culminate in chemoresistance and ultimately bowel obstruction, the most frequent cause of death. For women whose disease continues to respond to platinum-based drugs, the disease can often be controlled for 5 years or more. Targeted treatments such as antiangiogenic drugs or poly (ADP-ribose) polymerase inhibitors offer potential for improved survival. The efficacy of screening, designed to detect the disease at an earlier and curable stage remains unproven, with key results expected in 2015.

The histomorphology of Lynch syndrome-associated ovarian carcinomas: toward a subtype-specific screening strategy

Women with Lynch syndrome (LS) are at increased risk for the development of epithelial ovarian cancer (OC). Analogous to previous studies on BRCA1/2 mutation carriers, there is evidence to suggest a histotype-specific association in LS-associated OCs (LS-OC). Whereas the diagnosis of high-grade serous carcinoma is an indication for BRCA1/2 germline testing, in contrast, there are no screening guidelines in place for triaging OC patients for LS testing based on histotype. We performed a centralized pathology review of tumor subtype on 20 germline mutation-confirmed LS-OCs, on the basis of morphologic assessment of hematoxylin and eosin-stained slides, with confirmation by immunohistochemistry when necessary. Results from mismatch-repair immunohistochemistry (MMR-IHC) and microsatellite instability (MSI) phenotype status were documented, and detailed pedigrees were analyzed to determine whether previously proposed clinical criteria would have selected these patients for genetic testing. Review of pathology revealed all LS-OCs to be either pure endometrioid carcinoma (14 cases), mixed carcinoma with an endometrioid component (4 cases), or clear cell carcinoma (2 cases). No high-grade or low-grade serous carcinomas or mucinous carcinomas of intestinal type were identified. Tumor-infiltrating lymphocytes were prominent (≥40 per 10 high-powered fields) in 2 cases only. With the exception of 1 case, all tumors tested for MMR-IHC or MSI had an MMR-deficient phenotype. Within this cohort, 50%, 55%, 65%, and 85% of patients would have been selected for genetic workup by Amsterdam II, revised Bethesda Guidelines, SGO 10% to 25%, and SGO 5% to 10% criteria, respectively, with <60% of index or sentinel cases detected by any of these schemas. To further support a subtype-driven screening strategy, MMR-IHC reflex testing was performed on all consecutive non-serous OCs diagnosed at 1 academic hospital over a 2-year period; MMR deficiency was identified in 10/48 (21%) cases, all with endometrioid or clear cell histology. We conclude that there is a strong association between endometrioid and clear cell ovarian carcinomas and hereditary predisposition due to MMR gene mutation. These findings have implications for the role of tumor subtype in screening patients with OC for further genetic testing and support reflex MMR-IHC and/or MSI testing for newly diagnosed cases of endometrioid or clear cell ovarian carcinoma.

The contribution of deleterious germline mutations in BRCA1, BRCA2 and the mismatch repair genes to ovarian cancer in the population

The aim of this study was to estimate the contribution of deleterious mutations in BRCA1, BRCA2, MLH1, MSH2, MSH6 and PMS2 to invasive epithelial ovarian cancer (EOC) in the population. The coding sequence and splice site boundaries of all six genes were amplified in germline DNA from 2240 invasive EOC cases and 1535 controls. Barcoded fragment libraries were sequenced using the Illumina GAII or HiSeq and sequence data for each subject de-multiplexed prior to interpretation. GATK and Annovar were used for variant detection and annotation. After quality control 2222 cases (99.2%) and 1528 controls (99.5%) were included in the final analysis. We identified 193 EOC cases (8.7%) carrying a deleterious mutation in at least one gene compared with 10 controls (0.65%). Mutations were most frequent in BRCA1 and BRCA2, with 84 EOC cases (3.8%) carrying a BRCA1 mutation and 94 EOC cases (4.2%) carrying a BRCA2 mutation. The combined BRCA1 and BRCA2 mutation prevalence was 11% in high-grade serous disease. Seventeen EOC cases carried a mutation in a mismatch repair gene, including 10 MSH6 mutation carriers (0.45%) and 4 MSH2 mutation carriers (0.18%). At least 1 in 10 women with high-grade serous EOC has a BRCA1 or BRCA2 mutation. The development of next generation sequencing technologies enables rapid mutation screening for multiple susceptibility genes at once, suggesting that routine clinical testing of all incidence cases should be considered.

Analysis and comparison of somatic mutations in paired primary and recurrent epithelial ovarian cancer samples

The TP53 mutations have been proved to be predominated in ovarian cancer in a study from The Cancer Genome Atlas (TCGA). However, the molecular characteristics of recurrent ovarian cancers following initial treatment have been poorly estimated. This study was to investigate the pattern of somatic point mutations in matched paired samples of primary and recurrent epithelial ovarian cancers, using the OncoMap mutation detection protocol. We have adapted a high-throughput genotyping platform to determine the mutation status of a large panel of known cancer genes. OncoMap v.4.4 was used to evaluate genomic DNA isolated from a set of 92 formalin-fixed, paraffin-embedded (FFPE) tumors, consisting of matched paired samples of initially diagnosed and recurrent tumors from 46 epithelial ovarian cancer (EOC) patients. Mutations were observed in 33.7% of the samples, with 29.3% of these samples having a single mutation and the remaining 4.3% having two or more mutations. Among the 41 genes analyzed, 35 mutations were found in four genes, namely, CDKN2A (2.2%), KRAS (6.5%), MLH1 (8.2%) and TP53 (20.7%). TP53 was the most frequently mutated gene, but there was no correlation between the presence of mutation in any gene and clinical prognosis. Furthermore, somatic mutations did not differ between primary and recurrent ovarian carcinomas. Every mutation present in recurrent samples was detected in the corresponding primary sample. In conclusion, these OncoMap data of Korean EOC samples provide that somatic mutations were found in CDKN2A, KRAS, MLH1, and TP53. No differences in mutational status between primary and recurrent samples were detected. To understand the biology of tumor recurrence in epithelial ovarian cancer, more studies are necessary, including epigenetic modifications or additional mutations in other genes.

Review of findings in prophylactic gynaecological specimens in Lynch syndrome with literature review and recommendations for grossing

AIMS

Prophylactic hysterectomy with bilateral salpingo-oophorectomy is being increasingly undertaken in patients with Lynch syndrome (LS). The pathological features in such specimens are not well described and, unlike the SEE-FIM protocol for salpingo-oophorectomy specimens in BRCA1/2 mutation carriers and the gastrectomy grossing protocols for patients with CDH1 (E-cadherin) mutations, guidelines have not been devised for the grossing of prophylactic gynaecological specimens from LS patients. We aimed to review the pathological findings in a series of prophylactic gynaecological specimens from LS patients and develop guidelines for the grossing of these specimens.

METHODS AND RESULTS

We reviewed the pathological findings in 25 prophylactic gynaecological specimens from LS patients and audited the grossing protocols in different centres across Ontario, Canada. We found a 32% incidence of endometrial carcinoma or a precursor lesion; the two endometrial cancers identified were low-grade, low-stage endometrioid adenocarcinomas. To address the absence of guidelines for pathological examination, we undertook a literature review of gynaecological malignancies and incidental findings in prophylactic specimens in LS patients.

CONCLUSION

We provide recommendations regarding the grossing of such specimens which includes in-toto examination of the lower uterine segment, endometrium, ovaries and fallopian tubes with representative sampling of the cervix.

Prospective study of high-risk, BRCA1/2-mutation negative women: the 'negative study'

Background

We previously reported that women from high-risk families who tested negative for a BRCA1 or BRCA2 (BRCA1/2) mutation were four times more likely to develop breast cancer compared to women in the general population. Preventive measures and risk factors for breast cancer development in these high-risk women have not been evaluated to the same extent as BRCA1/2 positive women. Further, there is virtually no scientific evidence about best practices in their management and care. The proposed study will examine a role of genetic and non-genetic factors and develop the systems and parameters for the monitoring and surveillance necessary to help establish guidelines for the care of this high-risk population.

Methods/Design

To achieve our goals, we will assemble and follow a Canadian cohort of 1,000 cancer-free women with a strong family history breast cancer (defined as two or more relatives affected by breast cancer under the age of 50, or three or more relatives diagnosed with breast cancer at any age from one side of the family and with no BRCA1/2 mutation in the family). All eligible participants will be mailed a study package including invitation to participate, consent form, a research questionnaire to collect data regarding family history, reproductive and lifestyle factors, as well as screening and surgery. Usual dietary intake will be assessed by a diet history questionnaire. Biological samples including toenail clippings, urine and blood samples will be collected. These women will be followed every two years by questionnaire to update exposure information, screening practices, surgical and chemoprevention, and disease development.

Discussion

Findings from this study will serve to help establish clinical guidelines for the implementation of prevention, counseling, and treatment practices for women who face an elevated risk of breast cancer due to family history, but who do not carry a BRCA1/2 mutation.

Association between IHC and MSI testing to identify mismatch repair-deficient patients with ovarian cancer

OBJECTIVE

In epithelial ovarian cancer, concordance between results of microsatellite instability (MSI) and immunohistochemical (IHC) testing has not been demonstrated. This study evaluated the association of MSI-high (MSI-H) status with loss of expression (LoE) of mismatch repair (MMR) proteins on IHC and assessed for potential factors affecting the strength of the association.

METHODS

Tumor specimens from three population-based studies of epithelial ovarian cancer were stained for MMR proteins through manual or automated methods, and results were interpreted by one of two pathologists. Tumor and germline DNA was extracted and MSI testing performed. Multivariable logistic regression models were fitted to predict loss of IHC expression based on MSI status after adjusting for staining method and reading pathologist.

RESULTS

Of 834 cases, 564 (67.6%) were concordant; 41 were classified as MSI-H with LoE and 523 as microsatellite stable (MSS) with no LoE. Of the 270 discordant cases, 83 were MSI-H with no LoE and 187 were MSS with LoE. Both IHC staining method and reading pathologist were strongly associated with discordant results.

CONCLUSIONS

Lack of concordance in the current study may be related to inconsistencies in IHC testing methods and interpretation. Results support the need for validation studies before routine screening of ovarian tumors is implemented in clinical practice for the purpose of identifying Lynch syndrome.

Risk factors for ovarian cancers with and without microsatellite instability

OBJECTIVE

The objective of this study was to evaluate the association between microsatellite instability (MSI) status and (1) ovarian cancer risk factors and (2) the distribution of the specific histologic subtypes in a population-based sample of epithelial ovarian cancers.

METHODS

Participants were drawn from 3 population-based studies of primary epithelial ovarian cancer. Tumor DNA was analyzed using 5 standardized microsatellite markers to assess MSI status. Patients were divided into 3 groups (MSI-high, MSI-low, and MSI-stable) according to National Cancer Institute criteria. We compared the prevalence of specific known risk and protective factors among the 3 subgroups, including body mass index, smoking history, parity, BRCA1 and BRCA2 mutation status, past oral contraceptive use, and tubal ligation. Similarly, we compared the distribution of the histologic subtypes among the 3 subgroups.

RESULTS

A total of 917 ovarian cancer patients were included. One hundred twenty-seven (13.8%) cancers were MSI-high. Subgroup analyses according to smoking, body mass index, parity, past oral contraceptive use, and past tubal ligation did not reveal any statistically significant differences among the groups. Among the 29 patients with BRCA1 mutations, 20.7% had MSI-high cancers compared with 5.9% among 17 BRCA2-mutation patients. The proportions of different ovarian cancer histologic findings among the various MSI subgroups were similar.

CONCLUSIONS

The prevalence of risk and protective factors among ovarian cancer patients is similar for cancers with and without MSI. The distributions of MSI do not differ significantly among ovarian cancers with different histologic findings. Ovarian cancer patients with BRCA1 mutations had a 21% rate of MSI-high tumors, compared with 6% among patients with BRCA2 mutations, but this difference was not statistically significant.

Microarray expression profile analysis of long non-coding RNAs of advanced stage human gastric cardia adenocarcinoma

Gastric cardia adenocarcinoma (GCA) is a unique malignant tumor for its characteristics different from gastric and esophageal cancer epidemiologically and pathologically. The incidence of GCA has steadily increased for the last three decades and many patients are diagnosed with advanced stage because of the lack of typical and obvious symptoms at an early stage. To gain insight into the molecular mechanisms of GCA of advanced stage, we investigated the microarray expression profile of long non-coding RNAs of 12 advanced stage GCA patients. Long non-coding RNAs (lncRNAs) lack protein-coding potential and are over 200 bp in length. LncRNAs are known to be involved in the multifactor and multistep processes of tumor development and metastasis. In this study, we performed lncRNA transcriptome profiling of GCA biopsy tissue from 12 GCA patients who were confirmed by pathology to have developed lymph node metastasis and 12 paired non-cancerous gastric cardia tissues to determine if a gene expression profile unique to the lymph node metastasis group could be detected. Comparison of differentially expressed transcripts between the groups identified eight pathways that corresponded to down-regulated transcripts and 18 pathways that corresponded to up-regulated transcripts (p value cut-off 0.05). Gene ontology analysis showed that the up-regulated transcripts were most highly enriched in SRP-dependent cotranslational protein targeting to membrane, cytosolic ribosome, and structural constituent of ribosome, and the down-regulated transcripts were highly enriched in carboxylic acid transport, focal adhesion, and cation binding. This study shows that lncRNAs dysregulation exerts important roles in human GCA lymph node metastasis, indicating that lncRNAs are novel candidate biomarkers for the clinical diagnosis of advanced stage GCA and that could be targets for further therapy.