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8-Oxoguanine, a common mutagenic DNA lesion, generates G:C>T:A transversions via mispairing with adenine during DNA replication. When operating normally, the MUTYH DNA glycosylase prevents 8-oxoguanine-related mutagenesis by excising the incorporated adenine. Biallelic MUTYH mutations impair this enzymatic function and are associated with colorectal cancer (CRC) in MUTYH-Associated Polyposis (MAP) syndrome. Here, we perform whole-exome sequencing that reveals a modest mutator phenotype in MAP CRCs compared to sporadic CRC stem cell lines or bulk tumours. The excess G:C>T:A transversion mutations in MAP CRCs exhibits a novel mutational signature, termed Signature 36, with a strong sequence dependence. The MUTYH mutational signature reflecting persistent 8-oxoG:A mismatches occurs frequently in the APC, KRAS, PIK3CA, FAT4, TP53, FAT1, AMER1, KDM6A, SMAD4 and SMAD2 genes that are associated with CRC. The occurrence of Signature 36 in other types of human cancer indicates that DNA 8-oxoguanine-related mutations might contribute to the development of cancer in other organs.

MUTYH variants are differently distributed in geographical areas of the world. In MUTYH-associated polyposis (MAP) patients from North-Eastern Italy, c.933+3A>C (IVS10+3A>C), a transversion causing an aberrant splicing process, accounts for nearly 1/5 of all mutations. The aim of this study was to verify whether its high frequency in North-Eastern Italy is due to a founder effect and to clarify its impact on MUTYH transcripts and protein. Haplotype analysis and age estimate performed on members of eleven Italian MAP families and cancer-free controls provided evidence that c.933+3A>C is a founder mutation originated about 83 generations ago. In addition, the Italian haplotype associated with the c.933+3A>C was also found in German families segregating the same mutation, indicating it had a common origin in Western Europe. Altogether c.933+3A>C and the two common Caucasian mutations p. Tyr179Cys and p.Gly396Asp represent about 60% of MUTYH alterations in MAP patients from North-Eastern Italy, suggesting the opportunity to perform targeted molecular screening for these variants in the diagnostic setting. Expression analyses performed on lymphoblastoid cell lines supported the notion that MUTYH c.933+3A>C alters splicing causing the synthesis of a non functional protein. However, some primary transcripts escape aberrant splicing, producing traces of full-length transcript and wild-type protein in a homozygote; this is in agreement with clinical findings that suggest a relatively mild phenotypic effect for this mutation. Overall, these data, that demonstrate a founder effect and further elucidate the splicing alterations caused by the MUTYH c.933+3A>C mutation, have important implications for genetic counseling and molecular diagnosis of MAP.

BACKGROUND: Germline mutations in the STK11/LKB1 gene cause Peutz-Jeghers syndrome, an autosomal-dominantly inherited condition characterized by mucocutaneous pigmentation, hamartomatous gastrointestinal polyposis, and an increased risk for various malignancies. We here report the results of the first Italian collaborative study on Peutz-Jeghers syndrome. AIMS: To assess cancer risks in a large homogenous cohort of patients with Peutz-Jeghers syndrome, carrying, in large majority, an identified STK11/LKB1 mutation. METHODS: One-hundred and nineteen patients with Peutz-Jeghers syndrome, ascertained in sixteen different Italian centres, were enrolled in a retrospective cohort study. Relative and cumulative cancer risks and genotype-phenotype correlations were evaluated. RESULTS: 36 malignant tumours were found in 31/119 (29 STK11/LKB1 mutation carriers) patients. The mean age at first cancer diagnosis was 41 years. The relative overall cancer risk was 15.1 with a significantly higher risk (p<0.001) in females (22.0) than in males (8.6). Highly increased relative risks were present for gastrointestinal (126.2) and gynaecological cancers (27.7), in particular for pancreatic (139.7) and cervical cancer (55.6). The Kaplan-Meier estimates for overall cumulative cancer risks were 20%, 43%, 71%, and 89%, at age 40, 50, 60 and 65 years, respectively. CONCLUSION: Peutz-Jeghers syndrome entails markedly elevated cancer risks, mainly for pancreatic and cervical cancers. This study provides a helpful reference for improving current surveillance protocols.

Aims and background. Colorectal carcinoma patients from hereditary non-polyposis colorectal cancer families are suggested to have a better prognosis than sporadic colorectal carcinoma cases. Since the majority of hereditary non-polyposis colorectal cancer-related colorectal carcinomas are characterized by microsatellite instability due to germline mutations in DNA mismatch repair genes, this is consistent with the prolonged survival observed in sporadic microsatellite instability-positive colorectal carcinoma compared to microsatellite stable cases. However, a fraction of colorectal carcinoma cases belongs to families that, despite fulfilling the clinical criteria for hereditary non-polyposis colorectal cancer, do not carry mismatch repair gene mutations. Our aim was to verify to what extent the genotypic heterogeneity influences the prognosis of hereditary non-polyposis colorectal cancer patients. Methods. A survival analysis was performed on 526 colorectal carcinoma cases from 204 Amsterdam Criteria-positive hereditary non-polyposis colorectal cancer families. Enrolled cases were classified as MLITH-positive, MSH2-positive and mutation-negative, according to the results of genetic testing in each family. Results. Five-year survival rates were 0.73 (95% Cl, 0.66-0.80), 0.75 (95% CI, 0.66-0.84) and 0.62 (95% Cl, 0.55-0.68) for MLH1-positive, MSH2-positive and mutation-negative groups, respectively (logrank test, P= 0.01). Hazard ratio, computed using Cox regression analysis and adjusted for age, sex, tumor site and stage, was 0.71 (95% Cl, 0.51-0.981 for the mutation-positive compared to the mutation-negative group. Moreover, in the latter group, patients with microsatellite instability-positive colorectal carcinomas showed a better outcome than microsatellite stable cases (5-year survival rates, 0.81 and 0.60, respectively; logrank test, P = 0.006). Conclusions. Our results suggest that the prognosis of hereditary non-polyposis colorectal cancer-related colorectal, AIMS AND BACKGROUND: Colorectal carcinoma patients from hereditary non-polyposis colorectal cancer families are suggested to have a better prognosis than sporadic colorectal carcinoma cases. Since the majority of hereditary non-polyposis colorectal cancer-related colorectal carcinomas are characterized by microsatellite instability due to germline mutations in DNA mismatch repair genes, this is consistent with the prolonged survival observed in sporadic microsatellite instability-positive colorectal carcinoma compared to microsatellite stable cases. However, a fraction of colorectal carcinoma cases belongs to families that, despite fulfilling the clinical criteria for hereditary non-polyposis colorectal cancer, do not carry mismatch repair gene mutations. Our aim was to verify to what extent the genotypic heterogeneity influences the prognosis of hereditary non-polyposis colorectal cancer patients. METHODS: A survival analysis was performed on 526 colorectal carcinoma cases from 204 Amsterdam Criteria-positive hereditary non-polyposis colorectal cancer families. Enrolled cases were classified as MLH1-positive, MSH2-positive and mutation-negative, according to the results of genetic testing in each family. RESULTS: Five-year survival rates were 0.73 (95% CI, 0.66-0.80), 0.75 (95% CI, 0.66-0.84) and 0.62 (95% CI, 0.55-0.68) for MLH1-positive, MSH2-positive and mutation-negative groups, respectively (logrank test, P = 0.01). Hazard ratio, computed using Cox regression analysis and adjusted for age, sex, tumor site and stage, was 0.71 (95% CI, 0.51-0.98) for the mutation-positive compared to the mutation-negative group. Moreover, in the latter group, patients with microsatellite instability-positive colorectal carcinomas showed a better outcome than microsatellite stable cases (5-year survival rates, 0.81 and 0.60, respectively; logrank test, P = 0.006). CONCLUSIONS: Our results suggest that the prognosis of hereditary non-polyposis colorectal cancer-related co

Colon cancers arising in most patients with hereditary nonpolyposis colorectal cancer (HNPCC) show microsatellite instability ( MSI). BAT26, a quasimonomorphic polyA stretch located just 3' of MSH2 exon 5, is considered the most sensitive and specific marker of MSI. A total of 10 HNPCC families with large intragenic MSH2 deletions, encompassing exon 5 and intron 5, identified by multiplex ligation-dependent probe amplification (MLPA) were included in this study. The deletions under study were del1-16, del1-8, del1-7, del1-6, and del3-6, detected in 3, 1, 2, 3, and 1 families, respectively. Although all patients examined from these 10 families developed unstable tumours, 13/19 MSI-H tumours (68 %) surprisingly showed stability of BAT26. By MLPA and MSH2 sequence analyses of the BAT26-stable tumours, we demonstrated that the wild-type MSH2 allele was somatically inactivated by an identical large deletion, with complete loss of intron 5/BAT26 sequences at the tumour DNA level. We could infer that the apparent stability of BAT26 was due to the complete absence of target BAT26 sequences in the tumour sample, which results in exclusive amplification of contaminant normal DNA, containing a single copy of a wild-type stable BAT26 sequence. Identification of a subset of MSH2-related unstable tumours that are not recognized by analysis of BAT26 instability indicates that this marker should never be used alone for rapid MSI screening of HNPCC tumours. Moreover, our findings indicate that BAT26 stability in the context of MSI is strongly suggestive of the presence of a large intragenic MSH2 deletion.