Daily treatment (for 12 to 14 months) of 2-month-old nulliparous or 8-month-old multiparous C3H/HeJ mice with 0.1 mg of 2-bromo-α-ergocryptine (CB-154) or 6-methyl-8-β-ergoline-acetonitrile, efficacious inhibitors of prolactin secretion, markedly reduced the incidence of spontaneous mammary hyperplastic nodules and mammary tumors. CB-154 appeared to be more effective than 6-methyl-8-β-ergoline-acetonitrile in suppressing the incidence of mammary tumors; the ergot virtually prevented the appearance of mammary tumors in nulliparous mice. Daily treatment of 5-month-old estrogen-treated, ovariectomized-hysterectomized C3H/HeJ mice for 12 months with CB-154 also significantly reduced the incidence of hyperplastic nodules and mammary tumors when compared with ovariectomized-hysterectomized mice treated with the steroid alone. Daily treatment of multiparous C3H/HeJ mammary tumor-bearing mice with CB-154 or 6-methyl-8-β-ergoline-acetonitrile generally failed, however, to promote regression of the mammary tumors. Thus significant prophylaxis of early preneoplastic lesions by drug-induced hormone (prolactin) suppression, resulting in a marked reduction in mammary tumor incidence, has been demonstrated in this study.

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Presented at the Conference, “Early Lesions and the Development of Epithelial Cancer,” October 21 to 23, 1975, Bethesda, Md. Supported by NIH Research Grant CA-13777 and American Cancer Society Research Grant ET-59.

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