Epigenetic and Genetic Alterations in Low Grade Papillary Serous Carcinoma of the Ovary
F Abu Shahin, X Ji, P Hui, F Abudul-Karim, W Liu, B Yang. Cleveland Clinic, Cleveland, OH; Yale University, CT; Case Western Reserve University, Cleveland, OH
Background: Different genetic pathways exist between low grade and high grade papillary serous carcinoma (PSC) of the ovary. Genetic mutations of BRAF and Ras in low grade PSC and p53 mutations in high grade PSC have been reported. Epigenetic alteration in low grade PSC, however, has not been well characterized. We studied methylation profiles of 5 tumor suppressor genes in low grade PSC and correlated the methylation profiling with mutations of BRAF and K-Ras.
Design: Twenty-three patients with low grade PSC were included. All cases, except one, were stage III. Pathologic diagnosis was reviewed and clinicopathologic features were tabulated. Genomic DNA was extracted from paraffin embedded tissue. BRAF v600 and K-Ras at codons 12/13 mutations were tested using pyrosequencing SNP assay. After bisulfite conversion of unmethylated cytosine to uridine, methylation status of each of the 5 genes (RASSF1a, p16, E-Cadherine, MGMT and FGFR2) was evaluated using pyrosequencing quantitative methylation assay. Student t-test and Chi-square tests were applied for statistical analysis.
Results: Approximately 48% (11/23) of low grade PSC harbored methylation of at least one of three genes, RASSF1a 35% (8/23), E-cad 13% (3/23) and p16 13% (3/23). Methylation of MGMT or FGFR2 was not detected in low grade PSC (0/23). Methylation of RASSF1a was mutually exclusive with methylation of p16, but was concurrent with methylation of E-Cadherine. Genetically, 56.5% (13/23) of low grade PSC tumors harbored mutations of either BRAF v600 (3/23) or K-Ras at codons 12/13 (10/23). BRAF and K-Ras mutations were mutually exclusive. BRAF mutation was also mutually exclusive with DNA methylation in all except one case. In contrast, the majority (75%) of cases harboring RASSF1a methylation had concurrent K-Ras mutations. Taken genetic mutations and DNA methylation together, about 74% of low grade PSC had either mutations for BRAF or K-Ras or methylation of at least one of 3 genes (RASSF1a, p16 and E-Cadherine).
Conclusions: Both genetic and epigenetic alterations are involved in tumorigenesis of low grade PSC of the ovary. Among molecular alterations, BRAF and K-Ras mutations and RASSF1a methylation are the most common events (82%,14/17). Our study indicates that alteration of RAS-RAF-MEK pathway may play the most important role in pathogenesis of low grade PSC.
Monday, March 9, 2009 1:30 PM
Platform Session: Section C, Monday Afternoon