LOSS OF HETEROZYGOSITY ON CHROMOSOME-13 IS COMMON ONLY IN THE BIOLOGICALLY MORE AGGRESSIVE SUBTYPES OF OVARIAN EPITHELIAL TUMORS AND IS ASSOCIATED WITH NORMAL RETINOBLASTOMA GENE-EXPRESSION

We examined the frequencies of loss of heterozygosity on chromosome 13 in 77 primary ovarian epithelial tumors subdivided into cystadenomas, tumors of low malignant potential, low grade carcinomas, and high gra de carcinomas. Such losses were found in approximately 50% of high gra de carcinomas but were not detected in any of the other tumor subtypes (P < 0.0001), suggesting a strong association between these abnormali ties and the high grade carcinoma phenotype. The tumors were also exam ined for abnormalities in expression of the retinoblastoma susceptibil ity gene (RB). This was assessed by immunohistochemical staining of ar chival tumor sections with a polyclonal antibody directed against both the phosphorylated and the underphosphorylated forms of the RB protei n. Most of the tumors, including those with allelic deletions on chrom osome 13, showed normal RB nuclear protein staining patterns. We concl ude that loss of RB expression is not a frequent event in primary ovar ian carcinomas and that this gene is probably not the target of the fr equent allelic deletions on chromosome 13 found in high grade ovarian carcinomas.