title: Equine estrogen-induced mammary tumors in rats.
abstract: Long-term hormone replacement therapy is associated with an increased risk of breast, ovarian and endometrial cancers in women. Equine estrogens are a principal component of hormone replacement therapy; however, their tumorigenic potential toward mammary tissue and reproductive organs has not been extensively explored. A pellet containing equilin was inserted under the skin of female ACI rats and the development of mammary tumors was monitored. Histological examination revealed premalignant lesions such as apocrine metaplasia in whole-mount preparations of mammary gland from the equilin-treated rats. ACI rats given 10mg equilin developed palpable mammary tumors at 13 weeks of treatment, and 37.5% of the rats developed mammary tumors within 15 weeks. For 2.5mg equilin, palpable tumors were observed in 8.3% of the rats after 8 weeks' treatment; the frequency was lower than that (42.9%) observed with 2.5mg E(2). No tumors were observed in the untreated rats. Evidently, equilin is a mammary carcinogen, and this potential may be associated with development of breast and reproductive cancers in women receiving hormone replacement therapy.
authors.affiliation: Department of Pharmacological Sciences, State University of New York at Stony Brook, NY 11794-8651, USA.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Okamoto
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Liu
authors.forename: Naomi
authors.initials: N
authors.lastname: Suzuki
authors.forename: Kanako
authors.initials: K
authors.lastname: Okamoto
authors.forename: Hyo Jeong
authors.initials: HJ
authors.lastname: Kim
authors.forename: Y R Santosh
authors.initials: YR
authors.lastname: Laxmi
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Sayama
authors.forename: Shinya
authors.initials: S
authors.lastname: Shibutani
mesh_terms: D000818:Animals; D015914:Estrogen Replacement Therapy / Q000009:adverse effects; D004966:Estrogens, Conjugated (USP) / Q000633:toxicity*; D005260:Female; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000473:pathology; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced*; D051381:Rats; D011912:Rats, Inbred ACI
chemical_list: D004966:Estrogens, Conjugated (USP)