[Fetal breast estrogen receptor (ER) and breast cancer]

The estrogen receptor in bilateral breasts of 36 6 to 10-month fetuses (17 male, 19 female) were examined. All fetal breasts had ER positive cells (greater than 50-90%). The ER levels were similar regardless of sex and age. When the ER status of 84 female breast cancer patients was analysed, ER was considered as an essential but not the only etiologic factor in mammary carcinogenesis. A positive correlation between the degree of differentiation and the ER level of breast cancer cells was demonstrated and the ER level did not correlate with the clinical staging of breast cancer. The results are briefly discussed in relation to the rationale of hormonal therapy of breast cancer.