17beta-hydroxysteroid dehydrogenase 14 affects estradiol levels in breast cancer cells and is a prognostic marker in estrogen receptor-positive breast cancer. 
Estrogens have an important role in the progression of breast cancer.  The 17beta-hydroxysteroid dehydrogenase (17HSD) family has been identified to be of significance in hormone-dependent tissues.  17HSD1 and 17HSD2 are the main 17HSD enzymes involved in breast cancer investigated this far, but it is possible that other hormone-regulating enzymes have a similar role.  17HSD5 and 17HSD12 are associated with sex steroid metabolism, and 17HSD14 is a newly discovered enzyme that may be involved in the estrogen balance.  The mRNA expression of 17HSD5, 17HSD12, and 17HSD14 were analyzed in 131 breast cancer specimens by semiquantitative real-time PCR.  The results were compared with recurrence-free survival and breast cancer-specific survival of the patients.  The breast cancer cell lines MCF7, SKBR3, and ZR75-1 were transiently transfected with 17HSD14 to investigate any possible effect on estradiol levels.  We found that high 17HSD5 was related to significantly higher risk of late relapse in estrogen receptor (ER)-positive patients remaining recurrence-free later than 5 years after diagnosis (P = 0.02).  No relation to 17HSD12 expression was found, indicating that 17HSD12 is of minor importance in breast cancer.  Patients with ER-positive tumors with high expression levels of 17HSD14 showed a significantly better prognosis about recurrence-free survival (P = 0.008) as well as breast cancer-specific survival (P = 0.01), confirmed by multivariate analysis (P = 0.04).  Transfection of 17HSD14 in the human breast cancer cells MCF7 and SKBR3 significantly decreased the levels of estradiol, presenting an effect of high expression levels of the enzyme.