Analysis of Newly Identified and Rare Synonymous Genetic Variants in the RET Gene in Patients with Medullary Thyroid Carcinoma in Polish Population.

Gain-of-function germline mutations of the RET proto-oncogene are responsible for initiation of carcinogenesis within the thyroid gland and development of hereditary form of medullary thyroid carcinoma and MEN2 syndrome. Genotype-phenotype correlations are established for most RET mutations, but the importance of the synonymous changes in this gene remains debatable. We aimed to analyze RET gene variants in Polish population. Genetic testing for the RET gene variants was performed with standard methods in 585 people aged 1-85, including 448 patients with medullary thyroid carcinoma and 131 of their first- and second-degree relatives, as well as six patients suspected of MTC/MEN2. Besides the most frequent synonymous changes, p.Leu769Leu, p.Ser836Ser, and p.Ser904Ser, four rare changes-c.1827C>T (p.Cys609Cys), c.2364C>T (p.Ile788Ile), c.2418C>T (p.Tyr806Tyr), and c.2673G>A (p.Ser891Ser)-were found in the RET gene, in the Polish population. Two of the rare changes, p.Cys609Cys and p.Ile788Ile, had not been previously described. The frequency of molecular synonymous variants in the general population was evaluated by testing 400 anonymous blood samples of neonates. Our findings may contribute to a better understanding of the genetic diversity of the RET gene and the involvement of synonymous variants in this diversity.

PIK3CA mutations and amplification in endometrioid endometrial carcinomas: relation to other genetic defects and clinicopathologic status of the tumors.

Alterations of the PIK3CA gene occur in endometrial carcinomas, but their role in the carcinogenesis of those malignancies is still poorly understood. In this study, PIK3CA mutations and amplification in 196 endometrioid endometrial carcinomas and 20 endometrial hyperplasias were assessed by single-strand conformation polymorphism (PCR-SSCP), sequencing, and quantitative polymerase chain reaction. Results were correlated with mutations in the PTEN, KRAS, and CTNNB1 genes and with the clinicopathologic parameters of the tumors. PIK3CA mutations were found in 39 (20%) carcinomas. Six new mutations were identified. No PIK3CA mutations were found in endometrial hyperplasias. PIK3CA amplification was observed in 24 (12.2%) carcinomas and in 2 (10%) hyperplasias. The PIK3CA mutations and amplifications (with the exception of 6 cases) occurred independently. PIK3CA mutations were significantly associated with PTEN mutations (P = .0414) and tended to be associated with CTNNB1 (P = .0833), but not with KRAS mutations. Conversely, the PIK3CA amplifications significantly negatively correlated with PTEN mutations (P = .0038) and did not coexist with CTNNB1 and KRAS mutations. The PIK3CA mutations were significantly associated with poorly differentiated tumors (P = .0423). Interestingly, PIK3CA amplifications, but not mutations, were strongly associated with older age (≥63 years, P = .0018). Our data show that mutations and amplification of PIK3CA are significant genetic alterations in endometrioid endometrial carcinomas associated with adverse clinicopathologic parameters (grade and stage). These data also demonstrate that PIK3CA mutations cooperate with PTEN mutations, suggesting an additive effect to PTEN, whereas PIK3CA amplification can, as an isolated event, enable the development of those tumors. Moreover, for the first time, a possible role of PIK3CA amplification in initiation and progression of endometrial carcinomas in older women is suggested, but this preliminary suggestion requires further research.

TP53 mutations in endometrial cancers: relation to PTEN gene defects.

OBJECTIVE: The PTEN and TP53 genes participate in the carcinogenesis of many malignancies, but the role of both genes in endometrial carcinogenesis is not fully elucidated. The aim of the study was to determine the quality and the frequency of incidence of TP53 and PTEN gene mutations and to assess their coexistence in endometrial cancers. Besides that, the correlation was studied between the detected defects and clinicohistopathological characteristics of the studied endometrial cancers. METHODS: The study material included DNA isolated from 81 endometrial cancers. The incidence of TP53 and PTEN gene mutations was assessed using polymerase chain reaction-single-strand conformation polymorphism and sequencing techniques. The statistical analysis of the results was performed using [chi]2 test. RESULTS: In 64.2% of the 81 endometrial cancers, mutations occurred in TP53 and/or PTEN genes: in 16.1%, mutations occurred only in TP53; in 33.3%, only in PTEN gene; and in 14.8%, in both TP53 and PTEN genes. In 35.8% of cases, no mutations were found in these genes. No statistically significant relationship was found between the incidence of mutations in TP53 gene and that in PTEN gene (P = 0.986). The incidence of mutations in PTEN gene was higher in medium and poorly differentiated endometrial cancers than in well-differentiated ones and was statistically significant (G2 + G3 vs G1; P = 0.049). Besides that, mutations in PTEN gene occurred significantly more frequently in patients younger than 55 years than in older women (> or =55 years; P = 0.027). No similar differences were found in TP53 gene. CONCLUSIONS: The results of the study demonstrate that TP53 gene mutations occur in some of endometrioid endometrial cancers in the presence of PTEN gene mutations, suggesting that both these genes participate in the development of these tumors.

Molecular genetic defects in endometrial carcinomas: microsatellite instability, PTEN and beta-catenin (CTNNB1) genes mutations.

PURPOSE: The present study aims to assess the incidence of microsatellite instability (MSI) and mutations in the PTEN and beta-catenin (CTNNB1) genes in endometrial carcinomas and to analyze the detected defects in these factors in relation to each other and to the clinico-pathological features of tumors. MATERIALS AND METHODS: In a series of 56 endometrioid endometrial carcinomas, the status of MSI was determined using nine polymorphic markers, and mutations in all exons of the PTEN gene and in exon 3 of the CTNNB1 gene were evaluated by SSCP and sequencing methods. RESULTS: Microsatellite instability was found in 18 carcinomas (32.1%, MSI+); the remaining 38 tumors were microsatellite stable (MSI-). In 15 cases (26.8%), a loss of heterozygosity (LOH) at the studied microsatellite markers also occurred. In 29 carcinomas (51.8%), mutations were found in the PTEN gene and in nine tumors (16.1%) in the CTNNB1 gene. PTEN mutations occurred significantly more frequently in MSI+ than in MSI- tumors (77.8 vs. 39.5%, p = 0.007), but, except for one, none of them was attributable to MSI. In contrast, incidence of CTNNB1 mutations in MSI+ and MSI- tumors no significantly differed between themselves (16.7 vs. 15.8%, p = 0.760). Interestingly, mutations in the CTNNB1 gene most frequently coexisted with mutations in the PTEN gene (7/9, 77.8%). However, this finding requires future verification on a larger group of cases. The incidence of MSI and PTEN, but not CTNNB1 mutations, was significantly more common in poorly, than in well-to-moderately, differentiated tumors (G3 vs. G1 + G2; p = 0.042, 0.039 and 0.958, respectively). CONCLUSION: We conclude that most frequently occurring mutations in the PTEN gene may be a key event for the tumorigenesis of endometrioid endometrial carcinomas, while coexistence or absence of microsatellite instability or mutations in the CTNNB1 gene may reflect the heterogeneity of molecular mechanisms contributing to the development of these tumors.

Preliminary studies on DNA retardation by MutS applied to the detection of point mutations in clinical samples.

MutS ability to bind DNA mismatches was applied to the detection of point mutations in PCR products. MutS recognized mismatches from single up to five nucleotides and retarded the electrophoretic migration of mismatched DNA. The electrophoretic detection of insertions/deletions above three nucleotides is also possible without MutS, thanks to the DNA mobility shift caused by the presence of large insertion/deletion loops in the heteroduplex DNA. Thus, the method enables the search for a broad range of mutations: from single up to several nucleotides. The mobility shift assays were carried out in polyacrylamide gels stained with SYBR-Gold. One assay required 50-200 ng of PCR product and 1-3 microg of Thermus thermophilus his6-MutS protein. The advantages of this approach are: the small amounts of DNA required for the examination, simple and fast staining, no demand for PCR product purification, no labelling and radioisotopes required. The method was tested in the detection of cancer predisposing mutations in RET, hMSH2, hMLH1, BRCA1, BRCA2 and NBS1 genes. The approach appears to be promising in screening for unknown point mutations.

The coexistence of ERBB2, INT2, and CMYC oncogene amplifications and PTEN gene mutations in endometrial carcinoma.

PURPOSE: To evaluate the frequency of ERBB2, INT2 and CMYC oncogene amplifications and their coexistence with PTEN gene mutations in endometrial carcinomas. METHODS: In 54 endometrial carcinomas amplification of ERBB2, INT2 and CMYC was determined using differential polymerase chain reaction (dPCR), and mutations in all exons of PTEN were investigated by PCR-SSCP and direct sequencing methods. Results were correlated with clinicopathological features of tumors. RESULTS: In 31 out of 54 endometrial carcinomas (57.4%) genetic defects were found within the examined genes. Of all identified defects, mutations in PTEN and the amplification of CMYC were most frequent (26/54-48.1% and 10/54-18.5%, respectively). INT2 was amplified in 5.6% (3/54) of cases. In no case did we find ERBB2 amplification. In 77.4% (24/31) of cases only one gene was damaged. Of these, 20 cases showed only PTEN mutations, three cases only CMYC, and one case only INT2 amplification. In another seven out of 31 tumors (22.5%) defects in two or three genes coexisted simultaneously: PTEN and CMYC in five cases, CMYC and INT2 in one case, and PTEN, CMYC, and INT2 in one case. We found a number of interesting relations between the location of mutations within the PTEN sequence and the presence (+) or lack (-) of CMYC amplification. In the PTEN+CMYC- tumors the PTEN mutations were most frequent in exons 1-5, and less frequent in exons 7-8 (66.7% and 33.3%, respectively). In contrast, in the PTEN+CMYC+ carcinomas the PTEN mutations were found mainly in exons 7-8 (85.7%). PTEN mutations were equally frequent in both early and more advanced endometrial carcinomas. The CMYC amplification, however, was more frequent in advanced as compared to early tumors, although this difference did not reach statistical significance. CONCLUSIONS: Our data suggest that differences in the presence of genetic defects may reflect the different molecular pathways of endometrial carcinogenesis. These data also suggest that location of intragenic PTEN mutations and their coexistence with the CMYC amplification may play a crucial part in the development of various subtypes of endometrial carcinoma, but this preliminary suggestion requires further research.

Assessment of the quality and frequency of mutations occurrence in PTEN gene in endometrial carcinomas and hyperplasias.

The quality and frequency of mutations in PTEN gene were assessed in 59 carcinomas and 6 hyperplasias of the endometrium in women. Screening for mutations was done in all exons of PTEN gene by the PCR-SSCP analysis and DNA sequencing. Results were correlated with histological status and clinical features of endometrial carcinomas. In 45.8% (27/59) of carcinomas, 36 somatic mutations were detected in PTEN gene. In seven carcinomas, two mutations and in one carcinoma three mutations coexisted simultaneously. Moreover in 33.3% (2/6) of hyperplasia cases mutations were shown. Most identified mutations (57.9%) were present in exons 5 and 8, less frequently in exons 2 (15.8%) and 7 (13.2%) and they were least frequent in exons 1 and 3 (5.3% each). No mutations were found in exons 4, 6 and 9. Of all identified mutations, 73.7% of those resulting in truncated protein were present due to deletions, insertions and nonsense mutations. Missense mutations accounted for 13.2% of mutations and they were present only in exon 5. One point mutation (2.5%) was in intronic splice site. The remaining 10.5% of mutations were neutral polymorphisms. No statistically significant correlation were found between the frequency of PTEN gene mutations and the clinical stage of endometrial carcinomas. However, evident statistically significant, reverse correlation were observed between the frequency of mutations and the grade of morphological differentiation of the diseases (chi(2)=7.2393, alpha=0.0071). In conclusion, our data support the view that PTEN gene mutations are frequent events involved in development of endometrial carcinomas in women.