Oestrogen receptor alpha in female fetal, infant, and child mammary tissue.

Oestrogen receptor alpha (ER alpha) expression was studied in female mammary tissue from a series of 35 samples obtained post-mortem, ranging from fetuses of 13 weeks' gestation to prepubertal children of 12 years. Immunocytochemistry was performed on formalin-fixed tissue after microwave antigen retrieval. ER alpha was present in epithelial cell nuclei from the 30th week of gestation onwards and was markedly up-regulated shortly after birth. For up to 3 months thereafter, progesterone receptor was also expressed, indicative that the ER alpha was functional. During this period, ER alpha was also present in epithelial cell cytoplasm. From this perspective of the developing breast, it is suggested that an early postnatal component should be added to the prenatal oestrogen hypothesis; further, the significance of ER alpha cytoplasmic staining in the adult breast also merits review. Copyright 2000 John Wiley & Sons, Ltd.