Levels of Estrogen Receptor B Splice Variant (Erb Delta 5) Mrna Correlates with Progesterone Receptor in Breast Carcinomas

It is well known that breast tumors which are estrogen positive ER(+) are more likely to respond to hormone therapy. However, a certain percentage of ER(+)/PR(+) tumors do not respond to this therapy. Identification of the second estrogen receptor, named estrogen receptor beta (ER), as well as the existence of numerous isoforms/splice variants of both ER alpha and ER beta, suggests that a complex regulation of estrogen action exists. In this study, we analyzed the expression ratio of ER beta 1 isoform and ER beta Delta 5 splice variant mRNAs, and its correlation with ER/PR status by quantitative RT-PCR and clinical and histopathological parameters. We found that the relative proportion of ER beta Delta 5 in the total ER beta 1 transcript pool inversely correlates with the PR level (rho = -0,359, p LT 0,003, Spearman). It may be that the ER beta Delta 5 variant modulates the ERa activity of downstream targets. In addition, we suggest that the determination of the expression profiles of ER alpha and ER beta isoforms and splice variants in the defined groups of patients are necessary for elucidating their involvement in endocrine resistance