Maura Pieretti

Loss of heterozygosity and genomic instability in synchronous endometrioid tumors of the ovary and endometrium

Background. The unknown etiology of endometrioid carcinomas of the ovary and the relatively high frequency of a concomitant carcinoma of the endometrium in these patients warrants study of such tumors. The aim of this study was to identify the genetic alterations involved in endometrioid ovarian cancer development, and to determine whether primary tumors of the endometrium and synchronous primary endometrioid tumors of the ovary could be distinguished based on differing patterns of genetic alterations. The distinction of metastatic carcinoma of the ovary from other synchronous primary tumors is often difficult but has important therapeutic and prognostic implications.

Heterogeneity of Ovarian Cancer: Relationships Among Histological Group, Stage of Disease, Tumor Markers, Patient Characteristics, and Survival

Epidemiological studies have established associations between various reproductive factors and risk of ovarian cancer; it has also been observed that some of these risk factors are only associated with specific histological subgroups. To investigate the correlation of genetic alterations with these risk factors, we examined a consecutive series of 158 ovarian cancer cases treated at the University of Kentucky (1990–96). Common molecular genetic alterations (LOH on chromosome 17, P53 alterations, K-RAS mutations), histological and clinical characteristics of the disease, demographic patient information and survival were evaluated. These latter data were from the Kentucky Cancer Registry. Univariate analysis showed higher frequencies of chromosome 17 loss and P53 mutations in tumors of advanced stage and grade, and in older and post-menopausal women. Non-mucinous tumors were more likely to be classified as late stage, high-grade cancers, and to have chromosome 17 loss and P53 mutations. Survival analysis indicated that stage was the only independent significant variable. When stage was the outcome variable in multiple logistic regression analysis, histology and chromosome 17 loss were significantly associated with poor survival. This case-case study provides evidence that ovarian cancers of mucinous and non-mucinous histology are significantly different with respect to clinical characteristics, survival and molecular alterations. It also lends support to the hypothesis that ovarian cancer is a heterogeneous disease with distinct etiological factors and clinical outcomes, which may require different approaches to treatment.

The molecular basis of ovarian cancer.

Background. Molecular genetic studies of ovarian cancer have been limited by the inaccessible location of the ovary, the advanced stage of tumors available for analysis, and the lack of a well‐defined precursor lesion. However, genetic alterations important in ovarian tumorigenesis have been identified recently.

Genetic alterations on chromosome 17 distinguish different types of epithelial ovarian tumors

Epithelial tumors of the ovary are the most common ovarian tumors of adult women. They exist in several different histological patterns and exhibit varying degrees of aggressiveness. Molecular genetic studies in epithelial ovarian cancer have shown that loss of heterozygosity (LOH) for regions of chromosome 17 is a common event, probably reflecting the inactivation of one or more tumor suppressor genes present on this chromosome. We examined 87 sporadic epithelial ovarian tumors of different grade and histological type at 16 loci on this chromosome and found that 35% of them showed LOH for chromosome 17. Of these, 84% showed LOH for all informative markers, suggesting that loss of the entire chromosome 17 homologue may have occurred. Interestingly, chromosome 17 loss was observed frequently in serous tumors (49%), was less common in endometrioid tumors (15%), and was rare in mucinous tumors (4%) (P = .01 and P = .0002, respectively). Our findings support the concept that the histological subtypes of epithelial ovarian cancer may be the result of different molecular genetic events.

Challenge in the differentiation between attenuated familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer: Case report with review of the literature

The clinical differentiation between hereditary nonpolyposis colorectal cancer (HNPCC) and attenuated familial adenomatous polyposis (AFAP) is very difficult. The 62-yr-old proband presented with duodenal adenocarcinoma. His history of subtotal colectomy for colon cancer, the rarity of duodenal adenocarcinoma in the general population, and his family history of colon cancer made us suspect that he might have FAP. We investigated this family by obtaining medical records and performing gene analysis. The proband had only 10 adenomatous colon polyps when he underwent subtotal colectomy for the cancer, so classic FAP was excluded. His family history included rectal cancer in his brother at 69 yr of age, colon cancer in his mother at 75 yr, and colon cancer in one maternal cousin at 42 yr. Three months after we started to study this family, the probands 32-yr-old son presented with rectal cancer. His family fulfilled the Amsterdam criteria for HNPCC, but AFAP could not be excluded. Upon gene testing, the proband was negative for APC gene germline mutation, which made AFAP highly unlikely. Moreover, high microsatellite instability (MSI) was detected in his adenomas and cancer tissues. The fulfillment of Amsterdam criteria, the exclusion of FAP and AFAP, and the high MSI established the diagnosis of HNPCC in this family. We also summarize the differences between FAP, AFAP, and HNPCC; extend the graphic description of the MSI mechanism; and propose a diagnostic strategy for HNPCC.

Common polymorphisms and somatic mutations in human base excision repair genes in ovarian and endometrial cancers.

The purpose of this study was to determine whether the human APEX and OGG1 genes, encoding proteins important in base excision repair (BER) of DNA, contain nucleotide sequence polymorphisms or are mutated somatically in tumors from women diagnosed with ovarian or endometrial cancer. Based upon the analysis of germline DNA from 83 individuals, 63 with ovarian cancer and 20 with endometrial cancer, we found two missense polymorphisms in APEX (Q51H and D 148E) and two missense (A3P and S326C) and one intronic (Exon 5-15 bp) polymorphism in OGG1. The frequencies of the various alleles (in the ovarian and endometrial cancer patients combined) were 4.8% for 51-His and 56.2% for 148-Glu in APEX, and 1.0% for 3-Pro and 20.0% for 326-Cys in OGG1. Somatic mutations in APEX (P112L, W188X and R237C) were identified in three of 20 endometrial tumors, but no mutations were identified in APEX in 43 ovarian tumors, or in OGG1 at either tumor site. Given the crucial role of the APEX and OGG1 proteins in BER of oxidative DNA damage, the identified polymorphisms are good candidates for genetic epidemiologic studies of cancer susceptibility, while the finding that three of 20 (15%) endometrial tumors have somatic mutations in APEX suggests that inactivation of the BER pathway is important for the development of endometrial cancer in at least a subset of cases.

Molecular Genetic Changes in Human Epithelial Ovarian Malignancies

The frequent finding of loss of heterozygosity (LOH) for a specific chromosomal marker in tumor DNA compared to normal DNA suggests the presence of a closely linked tumor-suppressor gene. Using Southern blot analysis, 34 primary ovarian epithelial tumors were examined for the presence of tumor-specific allelic losses, using six probes for chromosomes 6q, 11p, 13q, 16q, and 17p. A high incidence of LOH was observed on 11p, 13q, and 17p. LOH for 17p was present in 3 of 4 (75%) informative benign ovarian tumors, 1 of 5 (20%) borderline tumors, and 16 of 24 (67%) invasive ovarian cancers. Allelic loss with the H-ras1 probe on 11p was present in 10 of 19 (53%) invasive tumors but was not identified in 6 benign or borderline tumors. LOH on 13q was present in 18 of 31 (58%) informative cases including 8 of 10 (80%) Stage 1 tumors. This preliminary study suggests that loss of tumor-suppressor genes on chromosomes 13q and 17p may be early events in ovarian tumorigenesis and that changes on chromosome 11p are later events.

Hypermethylation at a chromosome 17 "hot spot" is a common event in ovarian cancer.

Alterations of normal DNA methylation patterns have been reported in various types of human tumors. These alterations are represented by genome wide hypomethylation and by region specific hypermethylation. One commonly hypermethylated region is 17p13.3 (D17S5), the putative site of a tumor suppressor gene. In this study we report that hypermethylation at this locus occurs frequently (33%) in ovarian tumors. We reported previously that loss of chromosome 17 is a common event in serous epithelial ovarian tumors. A correlation of the methylation event and chromosome 17 loss suggests that hypermethylation at D17S5 precedes chromosome 17 loss.

Molecular evidence for the induction of large interstitial deletions on mouse chromosome 8 by ionizing radiation

The P19H22 mouse embryonal carcinoma cell line is characterized by a hemizygous deficiency for the chromosome 8 encoded aprt (adenine phosphoribosyltransferase) gene and heterozygosity for many chromosome 8 loci. We have previously demonstrated that this cell line is suitable for mutational studies because it is permissive of events ranging in size from base-pair substitutions at the aprt locus to apparent loss of chromosome 8. Large mutational events, defined by loss of the remaining aprt allele, were found to predominate in spontaneous mutants and those induced by ionizing radiation (Turker et al., Mutation Res., 329, 97–105, 1995). In this study we have used a PCR based assay to screen for loss of heterozygosity at microsatellite loci both proximal and distal to aprt in 137Cs-induced and spontaneous aprt mutants. This approach allowed us to distinguish apparent interstitial deletional events from apparent recombinational events. Significantly, 32.5% (26 of 80) of the mutational events induced by 137Cs appeared to be interstitial deletions as compared with 7.7% (6 of 78) in the spontaneous group. This difference was statistically significant (p<0.0001) suggesting that exposure to 137Cs caused a significant number of deletion mutations. Most 137Cs-induced interstitial deletions were larger than 6 cM, whereas none of the spontaneous deletions were larger than 6 cM. These results provide further support for the notion that ionizing radiation induces deletion mutations and validate the use of the P19H22 cell line for the study of events induced by ionizing radiation.

Evidence for a unifocal origin in familial ovarian cancer

OBJECTIVE The purpose of this investigation was to determine the pattern of loss of heterozygosity in multiple tumor sites from familial ovarian cancer cases. If ovarian cancer arises focally in one ovary and then metastasizes to other sites, a similar pattern should be seen in all tumor sites. However, if ovarian cancer arises multifocally throughout the peritoneal cavity, a different pattern of loss would be expected among the different sites. STUDY DESIGN The presence or absence of loss of specific alleles for 9 loci on chromosomes 1, 6, 11, 13, 16, and 17 was determined in multiple tumor sites from 12 familial ovarian cancer cases. RESULTS The frequency of loss of heterozygosity was as follows: chromosome 17 (100%), chromosome 13 (82%), chromosome 6 (80%), chromosome 16 (73%), chromosome 1 (57%), and chromosome 11 (22%). In every case an identical pattern was present for at least one locus. In four cases loss of the same allele was present in tumor from the ovary and all metastatic sites for all informative loci. In the remaining eight cases loss of the same allele for one to five (mean three) loci was detected. CONCLUSIONS The pattern of loss of heterozygosity in the 12 familial ovarian cancers included in this investigation favors a unifocal origin of disease. A dual primary origin could not be absolutely excluded in 3 cases. High frequencies on chromosomes 17q and 13 suggest that loss of whole or part of these chromosomes is important in ovarian carcinogenesis.