A study of the transition from premalignancy to clinical prostate cancer

Abstract

Prostate cancer remains the most commonly diagnosed life-threatening malignancy and the second leading cause of death from cancer in men. However, little is known about molecular mechanisms that underline its initiation and progression. The aim of this thesis is to characterize the involvement of three different genes and their protein products in human prostate cancer in the panel of clinical samples and established cell lines, in order to gain additional information about the development and progression of the disease. Additionally, a cytological characterization of prostatic intraepithelial neoplasia (PIN), a well established precursor of prostate cancer, has been done.

Paired tumor and constitutional DNA from prostate cancer patients has been used to perform mutational analysis of the BRG1 gene. In total, by combining SSCP and sequence analyses, DNA from twenty one patients has been screened. The analysis of all 35 BRG1 coding exons revealed the absence of somatic mutations, but presence of five SNPs, three of which were novel (Paper I).

In order to evaluate Pim-1 expression in human prostate cancer and prostatic intraepithelial neoplasia, immunohistochemical analysis has been done on an extended series of clinical samples. By previous studies, Pim-1 was shown to be involved in cell cycle regulation, and overexpression of Pim-1 protein was detected in prostate cancer. The results show a relative Pim-1 overexpression in HGPIN as compared to cancer. Upregulation of Pim-1 at premalignant stages suggests its involvement in the development of prostate cancer, possibly playing a role in the transition from precancerous lesions to invasive cancer. Additionally, Pim-1 expression may be a useful tool for distinguishing HGPIN from benign prostatic epithelium (Paper II).

A combination of immunohistochemistry and FISH analyses has been used to study protein expression and gene copy number of ezrin, a gene which is actively involved in the regulation of growth and metastatic capacity of cancer cells. The results show that ezrin has higher protein expression in HGPIN and prostate cancer as compared to normal prostate epithelium. However, FISH results did not reveal any copy number changes of this gene, indicating that ezrin protein overexpression cannot be explained by gene amplification. The data suggest that higher protein expression of ezrin in prostate cancer precursor lesions may indicate its involvement in the pathogenesis of the disease in its initial steps (Paper III).

Paper IV assessed ezrin immunostaining patterns in benign and malignant prostatic tissue in order to investigate possible correlations between its expression and histopathological and prognostic data. The results show the correlation of ezrin immunoreactivity with adverse prognostic factors, thus strengthening the hypothesis of the role of ezrin in prostate tumorigenesis.

A sampling method for simulating fine-needle aspiration cytology (FNAC) was used to characterize cytological features of PIN. This is believed to be the first attempt to describe PIN cytologically and distinguish it from invasive cancer. For this study, cancer-free specimens containing PIN were selected. Smears with invasive prostate cancer were used for comparison. Cancer smears showed high cellularity and dissociation of atypical cells, while PIN smears only contained a few clusters of atypical cells. Furthermore, pronounced nuclear atypia, prominent and multiple nucleoli and mucin were more common in the cancer. These results indicate that PIN should not be diagnosed by FNAC alone. However, a highly cellular smear with dissociated, distinctly atypical cells seems to preclude PIN (Paper V).

Collectively, the results of this study further characterize the process of transition from premalignancy to invasive prostate cancer and suggest possible early oncogenic events in the prostate.