Retinoic acid receptor-α （RAR α） plays a major role in the growth inhibitory effect of retinoic acid on human breast cancer cells

may be it could serve as an indicator to guide the treatment and prevent of breast cancer with retinoic acid in clinic. All previous researchs were based on observing the changes of RAR α mRAN expression. In this study

the expression of RAR α in human breast cell lines was studied by Northern Blot

Western Blot and Immunohistochemistry in mRNA level and protein level. Results showed that RAR α protein expression was correlated with RAR α mRNA expression. RAR α mRNA　ex- pression was higher in estrogen receptor （ER）-positive human breast cancer cell lines than in ER-negative ones. So was RAR a protein expression. Both RAR α mRNA amd RAR α protein expression were associ- ated with ER status. The expression of RAR α and the relationship between RAR a and ER status were al- so determined by immunohistochemistry in 58 human primary breast cancer tumors. 37 （63. 8% ） tumors were ER-positive and of these 28 （75. 7% ） were also RAR α -positive. The coexpression of ER and RAR a was statistically significant （P＜0. 01

by X

2

contingency analysis）. It was reported that RAR α expres- sion in cultured breast cancer cells was regulated by estrogen acting via the ER. Our study demonstrated that RAR α expression may be modulated in breast cancer in vivo by estrogen via ER.