Manuela Baptista

MSH6 germline mutations in early-onset colorectal cancer patients without family history of the disease

Germline MLH1 and MSH2 mutations are scarce in young colorectal cancer patients with negative family history of the disease. To evaluate the contribution of germline MSH6 mutations to early-onset colorectal cancer, we have analysed peripheral blood of 38 patients diagnosed with this disease before 45 years of age and who presented no family history of hereditary nonpolyposis colorectal cancer-related cancers. Blood samples from 108 healthy volunteers were analysed for those genetic alterations suspected to affect the function of MSH6. Of the seven (18.4%) MSH6 alterations found, we have identified three novel germline mutations, one 8 bp deletion leading to a truncated protein and two missense mutations resulting in the substitution of amino acids belonging to different polarity groups. High-frequency microsatellite instability was found in the patient with the MSH6 deletion, but not in the other 27 carcinomas analysed. No MLH1 promoter methylation was detected in tumour tissue. Our findings suggest that germline MSH6 mutations contribute to a subset of early-onset colorectal cancer. Further studies are warranted to understand the genetic and environmental factors responsible for the variable penetration of MSH6 germline mutations, as well as to identify other causes of early-onset colorectal cancer.

A novel exonic rearrangement affecting MLH1 and the contiguous LRRFIP2 is a founder mutation in Portuguese Lynch syndrome families

Purpose: Although Lynch syndrome is characterized by marked genetic heterogeneity, some specific mutations are observed at high frequency in well-defined populations or ethnic groups due to founder effects.Methods: Genomic breakpoint identification, haplotype analysis, and mutation age determination were performed in 14 unrelated patients and 95 family members presenting the same MLH1 exonic rearrangement, among a series of 84 Lynch syndrome families with germline mutations in MLH1, MSH2, or MSH6.Results: All 14 probands harbored an identical deletion, comprising exons 17–19 of the MLH1 gene and exons 26–29 of the LRRFIP2 gene, corresponding to the MLH1 mutation c.1896 + 280_oLRRFIP2:c.1750-678del. This mutation represents 17% of all deleterious mismatch repair mutations in our series. Haplotype analysis showed a conserved region of approximately 1 Mb, and the mutation age was estimated to be 283 ± 78 years. All 14 families are originated from the Porto district countryside.Conclusion: We have identified a novel MLH1 exonic rearrangement that is a common founder mutation in Lynch syndrome families, indicating that screening for this rearrangement as a first step may be cost-effective during genetic testing of Lynch syndrome suspects of Portuguese ancestry, especially those originating from the Porto district.

The MSH2 c.388_389del mutation shows a founder effect in Portuguese Lynch syndrome families.

The MSH2 c.388_389del mutation has occasionally been described in Lynch families worldwide. At the Portuguese Oncology Institute in Porto, Portugal, we have identified 16 seemingly unrelated families with this germline mutation. To evaluate if this alteration is a founder or a recurrent mutation we performed haplotype analysis in the 16 Portuguese index cases and 55 relatives, as well as in four index cases and 13 relatives reported from Germany, Scotland, England, and Argentina. In the Portuguese families we observed a shared haplotype of approximately 10 Mb and all were originated from the north of Portugal. These results suggest that this alteration is a founder mutation in Portugal with a relatively recent origin. In the reported families outside Portugal with this mutation different haplotype backgrounds were observed, supporting the hypothesis that it occurred de novo on multiple occasions. We also conclude that the high proportion of families with the MSH2 c.388_389del mutation indicates that screening for this alteration as a first step may be cost‐effective in the genetic testing of Lynch syndrome suspects of Portuguese ancestry, especially those originating from the north of Portugal.

TP53 germline mutations in Portugal and genetic modifiers of age at cancer onset

The Li-Fraumeni syndrome (LFS) is a rare, autosomal dominant disease caused by TP53 germline mutations. This study aimed to characterize the TP53 mutational spectrum in patients suspected to have LFS in Portugal and to evaluate the influence of the MDM2-SNP309 and TP53-72Arg variants and of telomere length on age of tumor onset. Probands were primarily selected using the classical LFS criteria (two cases) or the more sensitive Chompret Li-Fraumeni-like (LFL) criteria (13 cases), but 12 additional patients that did not comply with those LFS or LFL criteria were included in the analysis based on clinical suspicion (LFS suspects). Nine of the 27 probands (33.3%) presented germline TP53 mutations, two of them occurring de novo and two of them being novel. Three of the nine TP53 mutations were found in families that did not comply with any of the commonly used criteria for TP53 testing, leaving room to recommend the use of less stringent criteria. An association was found between the presence of the TP53-72Arg (but not the MDM2-SNP309) variant and earlier age of onset in TP53 carriers. A negative correlation between telomere length and age of cancer onset was found in patients with germline TP53 mutation, whereas no such correlation was found in controls or in patients with wild-type TP53.

Four Novel MSH2 / MLH1 Gene Mutations in Portuguese HNPCC Families

Hereditary non‐polyposis colorectal cancer (HNPCC) is considered to be determined by germline mutations in the mismatch repair (MMR) genes, especially MSH2 and MLH1. While screening for mutations in these two genes in HNPCC portuguese families, 3 previously unreported MSH2 and 1 MLH1 mutations have been identified in families meeting strict Amsterdam criteria. Hum Mutat 15:116, 2000.

Pathologic Findings in Prophylactic and Nonprophylactic Hysterectomy Specimens of Patients With Lynch Syndrome.

Women with Lynch syndrome (LS) have a high risk of developing endometrial carcinoma (EC) and, less frequently, ovarian carcinoma. As EC not uncommonly is the first malignancy, prophylactic hysterectomy (PH) has been increasingly implemented. In this study, we report the clinicopathologic features of a series of 70 LS patients who underwent either PH (n=39) or nonprophylactic hysterectomy (NPH) (n=31) at 3 tertiary referral centers. Among the 39 patients with PH, 2 had endometrial tumors seen grossly, whereas 37 showed no macroscopic lesions. Total inclusion of the endometrium was performed in 24/39 (61.5%). Abnormal histologic findings were identified in 9/39 (23.1%) PHs: 3 endometrial endometrioid carcinomas (EECs), including the 2 macroscopic and 1 microscopic (0.6 cm), and 4 atypical and 6 nonatypical hyperplasias. NPH included those performed for endometrial and ovarian cancer treatment. Tumor sampling followed standard protocols. ECs comprised 26 EECs and 1 clear cell carcinoma, with a median size of 3.7 cm. Hyperplasia was observed in 10 (33.3%) as background in EC, in 4 showing atypia. Eight (29.6%) tumors were centered in the lower uterine segment (all EECs). EECs were predominantly well differentiated (53.8%) and FIGO stage I (77.8%). A papillary architecture was common (51.9%) and associated with microcystic elongated and fragmented foci in 4. Mucinous differentiation was observed in 25.9% of endometrial tumors, typically representing <10%. Most endometrial tumors (81.5%) showed tumor-infiltrating lymphocyte counts ≥42/10 high-power fields. Four tumors showed extensive necrosis. Eight patients had ovarian tumors (4 synchronous), including 2 endometrioid carcinomas, 2 clear cell carcinomas, 1 borderline clear cell adenofibroma, 1 Müllerian carcinoma of mixed cell types, 1 primitive neuroectodermal tumor, and 1 metastatic melanoma. Total inclusion of the endometrium should be done in all LS patients’ surgical specimens without macroscopic lesions as some of these patients harbor preneoplastic or neoplastic conditions treatable at an early stage. The phenotype of LS-associated endometrial and ovarian tumors is variable and frequently includes features not commonly observed in sporadic cancers, but in our experience carcinomas were in general low grade and low stage.

Co-occurrence of nonsense mutations in MSH6 and MSH2 in Lynch syndrome families evidencing that not all truncating mutations are equal.

The majority of pathogenic mismatch repair (MMR) gene mutations detected in Lynch syndrome patients are truncating (frameshift or nonsense). However, the classification of terminal truncating mutations is sometimes difficult and predictive testing based on non-deleterious variants can have very serious consequences. Here, we report eight probands that have two germline nonsense mutations, namely MSH6 c.1030C>T, p.(Gln344Ter) and MSH2 c.2785C>T, p.(Arg929Ter), and one additional patient who presented only the MSH2 mutation previously reported as deleterious. The novel MSH6 truncating mutation was classified as deleterious, as it is predicted to encode a protein with loss of 1017 amino acid residues. The MSH2 mutation, which is expected to encode a protein lacking six amino acid residues, was considered a variant of unknown significance. Five tumors of the eight double-mutant individuals had normal MSH2 expression, whereas MSH6 immunoexpression was lost in all evaluable cases. None of the variants were detected in normal controls or associated with other MMR germline mutations in our series. This study emphasizes that not all truncating mutations are equal and that one must be cautious in the interpretation of the presumed deleterious effect of terminal frameshift or nonsense mutations.

Pathological features of total gastrectomy specimens from asymptomatic hereditary diffuse gastric cancer patients and implications for clinical management

Hereditary diffuse gastric cancer (HDGC) is an autosomal dominant syndrome characterised by multigenerational diffuse gastric cancer, and is mainly caused by germline alterations in the CDH1 gene. Currently, endoscopy has limited diagnostic accuracy, and total gastrectomy (TG) is the treatment of choice for asymptomatic CDH1 carriers. In this study, we aimed to obtain a better understanding of HDGC syndrome by exploring the histopathological findings of TG specimens from asymptomatic HDGC patients. A comprehensive literature review was carried out, searching for TGs performed in asymptomatic HDGC patients. Fourteen unpublished cases, analysed in our institution, were also included. The series encompassed 174 CDH1 carriers. Preoperative endoscopic biopsies were positive in 28.3%. A macroscopic lesion was apparent in 11.7% of TGs. Histopathological analysis revealed intraepithelial lesions and/or intramucosal signet ring cell carcinoma in 87.9% of TGs. When we explored the type of protocol used for handling the specimens, we found that microscopic cancer foci were detected in 95.3% of TGs when a total‐embedding protocol (assessment of the totality of gastric mucosa) was applied, and only in 62.5% when no specific protocol was used (P < 0.001). Helicobacter pylori infection was found in 23.4% cases. In conclusion, a thorough histopathological examination of gastric mucosa remains the gold standard for detection of cancer foci in HDGC gastrectomy specimens, requiring experienced pathologists for an accurate diagnosis. A better understanding of the natural history of HDGC will enable better clinical management of HDGC patients, particularly regarding the optimal timing for the performance of TG.