Since the discovery of estrogen receptor-β (ER-β), five C-terminal variants of ER-β were identified. We designed this study to investigate the pattern and clinical implications of ER-β and its splicing variants expression in normal and malignant mammary tissues.

Using reverse transcription polymerase chain reaction (RT-PCR), we examined the expression levels of ER-α and ER-β and its five splicing variants (β1, β2, β3, β4, β5) in 50 paired normal and cancer tissues. We measured the densities of RT-PCR products using Tina version 2.10 (Raytest, Germany). Firstly, the incidence and intensity of ER-α and ER-β and its five splicing variants were compared. Then the expression of ER-β mRNA splicing variants was also analyzed with regard to the ER-α protein expression measured by immuno-histochemical staining and the menopausal status of the patients. Chi-square test and paired samples t-test were used for statistical analysis. Differences were considered to be significant with a p-value of less than 0.05.

The expression of ER-β mRNA variants in normal breast and cancer tissues were as follows: ER-β2 (100%/100%), ER-β4 (76%/74%), ER-β5 (32%/58%), and ER-β1 (14%/16%). ER-β3 was not detected at all. In terms of intensity, we observed a significant decrease of ER-β2 (P<0.001) and an increase of ER-β5 (P=0.004) in the mRNA expression levels among breast cancers compared to the corresponding normal breast tissues. Compared to the corresponding normal tissues, a significant decrease of ER-β2 in cancer tissues was observed in patients with ER-α-positive (P<0.001), with age over 50 (P=0.01), and under 50 (P=0.04) as well, but not in patients with ER-α-negative (P=0.48). ER-β4 also significantly decreased in patients with ER-α-positive (P=0.004) and with age over 50 (P=0.07). ER-β5 showed a significant increment only in patient aged over 50 (P=0.04).

ER-α mRNA expression significantly increases but ER-β mRNA expression decreases in the cancer tissues compared to the corresponding normal tissues. Among ER-β variant forms, ER-β2 is predominant in both normal and malignant mammary tissues and ER-β4, ER-β5, and ER-β1 in descending order but ER-β3 does not express in mammary tissues. The decrease of ER-β2 and ER-β4 expression is prominent in cancer tissue especially in ER-α-positive cancers, which suggests that ER-β2 and ER-β4 may possess a regulatory function in mammary carcinogenesis. Further investigations to verify the roles of ER-β variants are mandatory.