Microvessel density and CpG island methylation of the THBS2 gene in malignant ovarian tumors

We aimed to investigate the role of thrombospondin-2 (THBS2) related angiogenic activity in malignant ovarian tumors and to determine if aberrant methylation associated inactivation is involved in down-regulating THBS2 expression in ovarian cancer. The methylation status of the THBS2 promoter region and microvessel density (MVD) was studied in 70 malignant ovarian tumors and in 15 control ovarian samples. A methylation specific PCR (MSP) method was used to distinguish methylated from unmethylated DNA in the promoter regions of the THBS2 gene. MVD was assessed with anti-CD34 antibodies and the results were compared between tumors with average (AVD) and high (HVD) microvessel density. Alterations in the expression of trombospondin-2 were more often seen in early (FIGO stage I and II ) than in late stage tumors (66% vs. 30%, p=0.01). Age, menopausal status, the histological type and tumor grade did not correlate with thrombospondin-2 expression, however, silencing of THBS2 gene was more often seen in higher rather than in lower grade (50% vs. 28%) cancers and in nonserous rather than in serous (43% vs. 32%) tumors. In 81% of THBS2 mRNA-negative tumors, ahypermethylated promoter region of THBS2 was found (p=0.00003). An unmethylated product of the MSP reaction was more often detected in high grade tumors (93% vs. 76%, p=0.04). The incidence of THBS2 hypermethylation was not related to the tumor histological type, but unmethylated THBS2 was more often found in serous rather than in nonserous tumor (96% vs. 74%, p=0.01). The median MVD in malignant the tumor samples was 21,7 (range: 7.6-55.2). In the group with HVD, 54% were THBS2 mRNAnegative, conversely, in the group with AVD tumors only 26% of the cases had undetectable THSB2 mRNA. A significant correlation between microvessel density and the expression of trombospondin-2 (p=0.009) was found. In the samples with HVD, 51% had hypermethylated THBS2, however methylation pattern had no significant influence on microvessel density. In conclusion, hypermethylation might be responsible for altered expression of thrombospondin-2 in ovarian cancer. The THSB2 methylation pattern had no significant influence on microvessel density.