Quantitative Analysis of Novel Prostate Cancer Markers in Tissue

Prostate cancer is a heterogeneous disease affecting an increasing number of men all over the world, but particularly in the countries with the Western lifestyle. The best biomarker assay currently available for the diagnosis of the disease, the measurement of prostate specific antigen (PSA) levels from blood, lacks specificity, and even when combined with invasive tests such as digital rectal exam and prostate tissue biopsies, these methods can both miss cancers, and lead to overdiagnosis and subsequent overtreatment of cancers. Moreover, they cannot provide an accurate prognosis for the disease. Due to the high prevalence of indolent prostate cancers, the majority of men affected by prostate cancer would be able to live without any medical intervention. Their latent prostate tumors would not cause any clinical symptoms during their lifetime, but few are willing to take the risk, as currently there are no methods or biomarkers to reliably differentiate the indolent cancers from the aggressive, lethal cases that really are in need of immediate medical treatment. This doctoral work concentrated on validating 12 novel candidate genes for use as biomarkers for prostate cancer by measuring their mRNA expression levels in prostate tissue and peripheral blood of men with cancer as well as unaffected individuals. The panel of genes included the most prominent markers in the current literature: PCA3 and the fusion gene TMPRSS2-ERG, in addition to BMP-6, FGF-8b, MSMB, PSCA, SPINK1, and TRPM8; and the kallikrein-related peptidase genes 2, 3, 4, and 15. Truly quantitative reverse-transcription PCR assays were developed for each of the genes for the purpose, time-resolved fluorometry was applied in the real-time detection of the amplification products, and the gene expression data were normalized by using artificial internal RNA standards. Cancer-related, statistically significant differences in gene transcript levels were found for TMPRSS2-ERG, PCA3, and in a more modest scale, for KLK15, PSCA, and SPINK1. PCA3 RNA was found in the blood of men with metastatic prostate cancer, but not in localized cases of cancer, suggesting limitations for using this method for early cancer detection in blood. TMPRSS2-ERG mRNA transcripts were found more frequently in cancerous than in benign prostate tissues, but they were present also in 51% of the histologically benign prostate tissues of men with prostate cancer, while being absent in specimens from men without any signs of prostate cancer. PCA3 was shown to be 5.8 times overexpressed in cancerous tissue, but similarly to the fusion gene mRNA, its levels were upregulated also in the histologically benign regions of the tissue if the corresponding prostate was harboring carcinoma. These results indicate a possibility to utilize these molecular assays to assist in prostate cancer risk evaluation especially in men with initially histologically negative biopsies.