Estrogen signal transduction plays very important roles in both normal mammary development and neoplastic progression. Since the discovery of estrogen receptor-β (ER-β) there have been many controversial reports on the role of ER-βin breast carcinogenesis and progression, and prognostic implications. ER-β mRNA levels were investigated in various mammary tissues in order to verify the role of ER-β expression in breast carcinogenesis.

Using messenger RNA (mRNA) in situ hybridization, we examined ER-β expression in 60 paired normal and cancer tissues, 11 paired normal and benign breast tumor tissues, and 10 metastatic lymph nodes. We determined the intensity and extent (proportion of cells with positive hybridization) of the mRNA hybridization signals and gave scores 0 to 3; no hybridization (0), minimal (1), moderate (2), and strong (3) by the hybridization intensity and no hybridization (0), hybridization in less than 10% of cells (1), 10~50% (2), and more than 50% of cells (3) by the proportion of positively hybridized cells. Chi-square test, independent t-test or one-way ANOVA test was used for the statistical analysis and differences were considered to be significant with a p-value of less than 0.05.

There was no statistically difference in ER-β expression between normal and benign mammary tissues. ERβ expression was significantly decreased in breast cancer and metastatic lymph node tissues compared with normal mammary and benign breast tumor tissues (P<0.01). The intensity and extent of ERβ expression were also significantly lower in breast cancer and metastatic lymph node tissues than in the normal mammary and benign breast tumor tissues (P<0.01). In cases of positive hybridization, the sum of scores of intensity and area were also significantly higher in normal and fibroadenoma tissues than in cancer or metastatic lymph nodes (P<0.01).

ERβ transcription decreases in the process of breast cancer development, which suggests a protective role of ERβ in breast carcinogenesis.