Molecular genetic characterization of clear cell carcinoma of the endometrium in comparison to endometrioid and serous carcinoma

The goal of this project is to determine molecular genetic changes involved in the development of clear cell carcinoma which is a histopathological subtype of endometrial carcinoma. Recent molecular studies have demonstrated differences in the patterns of molecular genetic alterations between endometrioid carcinoma, the most common histopathological subtype of endometrial carcinoma and the less common serous carcinoma. We have recently shown that clear cell carcinoma has a distinctive immunoprofile if compared to serous and endometrioid carcinoma although there are histological and biological similarities between serous carcinoma and a subset of clear cell carcinoma. In particular, clear cell carcinoma as well as serous carcinoma are characterized by low estrogen and progesterone receptor expression and high Ki-67 expression but clear cell carcinoma expresses p53 to a significantly lower degree than serous carcinoma. Therefore, we hypothesized that the development of clear cell carcinoma might be driven by different molecular genetic mechanisms. This proposal includes several experimental steps to test our hypothesis by analyzing the molecular genetic profile of clear cell carcinoma of the endometrium and comparing it with serous and endometdoid carcinoma. First, clear cell carcinoma will be analyzed for molecular genetic alterations that have been previously determined in serous and endometrioid carcinoma, in particular K-ras and p53 mutations and microsatellite instability (MI). In addition, clear cell carcinoma will be analyzed for gross chromosomal aberrations by comparative genomic hybridization (CGH) and the findings will be compared to serous and endometrioid carcinoma. These analyses will further include different histological subtypes of clear cell carcinoma, endometrioid carcinoma and oxyphilic cell differentiation associated with clear cell carcinoma and putative precursor lesions such as atypical hyperplasia and endometrial intraepithelial carcinoma (EIC). Furthermore, clear cell carcinoma will be analyzed for loss of heterozygosity (LOH) at multiple chromosomal arms. LOH analysis has the potential to detect chromosomal loci harboring novel genes that may be involved in tumorigenesis. The combination of CGH and LOH analysis will allow us to obtain information on both gross and subtle genomic alterations. Moreover, information obtained by LOH will also gain increasing importance in the future since the human genome will be rapidly explored by the human genome project. Known genes associated with loci showing high LOH frequency will be main targets for mutational analysis. As a future perspective, loci of genomic alterations will be further analyzed by fluorescent in situ hybridization (FISH). Although clear cell carcinoma accounts only for a small number of endometrial carcinomas, a comparison of its molecular genetic profile with that of endometrioid and serous carcinoma may contribute to a better understanding of the development of the different histopathological and biological types of endometrial carcinoma. We further believe that this study has the potential to provide novel information that can be useful for the development of novel therapeutical and diagnostic strategies of endometrial carcinoma.

Uterine cancer (endometrial carcinoma) can be subdivided in various types of cancer by a histological examination under the light microscope. The most frequent subtype is endometrioid carcinoma whereas other types such as serous carcinoma are rare. It is important to emphasize that these subtypes are also distinctive by their clinical behaviour. Endometrioid carcinoma behaves usually in a favourable manner whereas serous carcinoma behaves aggressively. This project analysed a rare group of endometrial carcinoma with aggressive behaviour and poor clinical outcome. These tumours are characterized by clear cells and therefore called clear cell carcinoma. Our investigations showed that clear cell carcinomas are closer related to the rare serous carcinoma than to the common endometrioid carcinoma. Like serous carcinomas they rarely harbour K-RAS mutations and microsatellite instability but in contrast to serous carcinoma they show significantly less mutations of the important tumour suppressor gene p53. Clear cell carcinoma is also genetically distinctive from secretory carcinoma which show similarities under the light microscope by both consisting of clear cells. Secretory carcinoma less frequently shows p53 mutations and loss of heterozyhosity (LOH) at multiple chromosomes but more frequently microsatellite instability compared to clear cell carcinoma. A high frequency of LOH is often related to mutations in important tumour suppressor genes. Interestingly, there may be genetic similarities between clear cell and secretory carcinoma: Both show a frequent loss of PTEN expression associated with frequent LOH at the chromosome arm that harbours the PTEN gene. It is important to mention that PTEN alterations are typical for endometrioid carcinoma but not for serous carcinoma. PTEN alterations are already found in precursors of endometrioid carcinoma. Our study shows that molecular genetic enables us to compare the genotyp and the phenotyp of tumours. There is evidence that particular changes of the genotyp might result in a particular phenotyp.