Abstract : Our previous work demonstrated that prostate cancers differ from benign prostatic epithelium by expressing oncogenic members of the pp32 gene family. Whereas benign prostatic epithelium solely expresses pp32, prostate cancers express pp32r1 and pp32r2, which are oncogenic. The purpose of the study was to confirm and extend these preliminary results, to develop practical means to assay pp32 gene family members in clinical samples, and to determine the clinical significance of their presence. The approved proposal encompassed four broad tasks: 1 characterization of the pp32 expression phenotype of a larger sample of 40 prostatic adenocarcinomas; 2 development of a practical molecular pathology assay for altered pp32 transcripts; 3 adaptation of the assay to paraff in- embedded tissue; and 4 preliminary determination of the clinical utility of pp32r1 and pp32r2 expression in prostatic adenocarcinoma. In the course of developing these previously reported assays, a mutation in pp32r1 was detected in a human prostatic cancer cell line in pp32r1 involving a T to C transversion at position 418; transfection studies showed this to cause increased cell proliferation. A PCR assay is now being used to determine the frequency of the pp32r1 mutation in prostate cancers. Antibodies will be used to examine pp32 gene family expression in prostate cancers.