Microsatellite Instability in Chinese Epithelial Ovarian Carcinoma. X.S. Liu¹, Y. Lu¹, N. Zhong^2,3. 1) Dept. Gynecology, OBGYN Hospital, Shanghai, China; 2) Peking University Center of Medical Genetics; 3) New York State Institute for Basic Research.
   Ovarian carcinoma (OC) is one of the most lethal cancers of women in China. About 90% of OC are epithelial ovarian tumors. The association of microsatellite instability (MSI) with several cancers has been shown to play a significant role in the development of cancers. However, The role and incidence of MSI in ovarian cancer are matters of great controversy. In some studies, MSI frequencies have ranged from 0 to 53% in sporadic ovarian cancers. These studies varied greatly in terms of the type and number of loci studied, the criteria used for defining MSI, and the histological subtypes of ovarian cancer analyzed. The role and incidence of MSI in epithelial ovarian tumor remains unknown. Our current study is to evaluate the frequency of MSI in epithelial ovarian tumors and its relationship with clinicopathologic features. Ninety fresh specimens of epithelial ovarian tumors (primary 74, secondary 16) were collected from our gynecology clinic of Medical Center of Fudan University from 2004 to 2005. Microsatellite analysis was carried out using 5 mono- and dinucleotide markers from the National Cancer Institute Consensus Panel by fluorescence-labeled polymerase chain reaction. Of the 90 epithelial ovarian tumors analyzed, 18 demonstrated a high level of MSI (MSI-H), 30 demonstrated a low level of MSI (MSI-L), and the remaining 42 exhibited microsatellite stability (MSS). Frequency of MSI at loci BAT-25 was higher than that at any other loci. No correlation was found between MSI level and patient age, tumor type, tumor differentiation (P >0.05). But the microsatellite instability-high phenotype correlate with clinical stage, it tended to occur more frequently in early-stage tumors (P=0.03). Our results indicate that there are frequent MSI in epithelial ovarian tumors. It is an early event and it is involved in the development of epithelial ovarian tumors.