Estrogens play a central role in the development of breast cancer. Most breast carcinomas are detected after menopause and despite a low degree of ovarian estrogen production and low levels of serum estrogen these tumors show a high in situ level of estrogens. Enzymes modulating local steroid availability seem to play an important role in the progression of especially estrogen receptor positive breast cancer. The 17ß-hydroxysteroid dehydrogenase (17ß-HSD) enzymes are involved in the interconversion of biologically active and inactive sex steroids and are considered to play a critical role in the in situ metabolism of estrogen.
The aim of this thesis was to investigate the expression of 17ß-HSD type 1 and 2 in breast cancer and correlate this to prognosis, and to analyze if the gene encoding 17ßHSD type 1 exhibits altered gene copy number in breast cancer. We also wanted to examine if the protein levels of aromatase, 17ßHSD type 1 and 17ßHSD type 2 show association with the expression of COX-2 in breast tumors and whether these proteins correlate to prognosis. Real-time RT-PCR was used to detect the rnRNA levels of 17ßHSD type 1 and type 2, and immunohistochemistry to detect the protein expression. To analyze if the gene encoding 17ßHSD type 1 exhibits altered gene copy number in breast cancer we used real-time PCR and genomic DNA.
While 17ßHSD type 1 catalyzes the conversion of estrone to the more potent estradiol, the type 2 enzyme catalyzes the opposite reaction. All tumors investigated in this study exhibited detectable rnRNA levels of 17ßHSD type 1. We found detectable rnRNA levels of 17ßHSD type 2 in the normal breast tissue, whereas many tumors lacked expression of type 2, especially among ER-positive tumors. In Paper I the expression of 17ßHSD type 2 was detectable in 14% of the tumors and in Paper III 17ßHSD type 2 mRNA was detected in 69% of the tumors. The expression of 17ßHSD type 2 seems to be lost in a subset of the breast tumors.
In Paper II we found amplification of the gene coding for 17ßHSD type 1 in 14.5% of the cases. HSD17B1 amplification had prognostic significance, and in particular, for ER-positive patients who received tamoxifen treatment, increased gene copy number indicated a decreased breast cancer survival. There was a significant correlation between HSD17B1 gene copy number and mRNA expression level of 17ßHSD type 1, when analyzing a subgroup of the patients.
In Paper II, among ER-positive patients, those with low expression of type 2 had a significantly higher recurrence rate compared with patients who expressed normal levels and this difference could not be seen among ER-negative patients. The prognostic significance of type 2 hold true in multivariate analysis. In Paper I, patients with late relapse in their disease more frequently had lost the mRNA expression of 17ßHSD type 2 than had matched control patients. In Paper IV, patients with ER-positive breast tumors with low protein levels of 17ßHSD type 2 had a worse prognosis, both concerning distant recurrence and breast cancer related death. In Paper I a high mRNA level of 17ßHSD type 1 predicted late relapses among breast cancer patients, however, in Paper IV a prognostic value of 17ßHSD type 1 could not be detected. In Paper III, there was no significant association between 17HSD type 1 and recurrence-free survival if the entire follow-up period was considered. However, for ER-positive patients still recurrence-free after 5 years, high levels of 17HSD type 1 was associated with a significantly higher rate of late relapse in the disease. When 17ßHSD type 1 and 2 were considered together, the expression ratio was a significant prognostic variable.
COX-2 protein expression was significantly correlated to aromatase, 17ßHSD type 1 and 17ßHSD type 2 levels, and this suggests that COX-2 might contribute to the upregulation of steroid converting enzymes. However, any significant prognostic value of COX-2 or aromatase could not be detected.
In summary, these results suggest that 17ß-HSD type 1 and 2 have prognostic importance in estrogen dependent breast cancer.
Linköping: Linköpings universitet , 2005. , 76 p.