'Oestetrol stimulates proliferation and oestrogen receptor expression in breast cancer cell lines: Comparison of four oestrogens.' abstract https://www.ncbi.nlm.nih.gov/pubmed/25213195
"Some current investigations suggest that the use of E4 in hormone therapy or contraception may have advantages in terms of breast cancer risk when compared to other oestrogens."
"Oestetrol was significantly less effective than E2 at the lower concentration."
"However, no difference was found regarding receptor expression [among estrogens]."
Oestetrol = Estetrol = 15-alpha-hydroxyoestriol = E4
Estriol = Oestriol = E3
"Some current investigations suggest that the use of E4 in hormone therapy or contraception may have advantages in terms of breast cancer risk when compared to other oestrogens."
"Oestetrol was significantly less effective than E2 at the lower concentration."
"However, no difference was found regarding receptor expression [among estrogens]."
Oestetrol = Estetrol = 15-alpha-hydroxyoestriol = E4
Estriol = Oestriol = E3