Equine estrogen-induced mammary tumors in rats.
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.
Okamoto
Yoshinori
Y
Department of Pharmacological Sciences, State University of New York at Stony Brook, NY 11794-8651, USA.
Liu
Xiaoping
X
Suzuki
Naomi
N
Okamoto
Kanako
K
Kim
Hyo Jeong
HJ
Laxmi
Y R Santosh
YR
Sayama
Kazutoshi
K
Shibutani
Shinya
S
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
D004966:Estrogens, Conjugated (USP)