MTW9, a transplantable mammary tumor in Wistar Furth rats, shows little growth unless host serum prolactin is increased. This study compares the response to ovariectomy of MTW9-MtT, a tumor developed in rats bearing the mammosomatotropic tumor MtTW10 (serum prolactin 500 to 7000 ng/ml) with MTW9-P developed in rats given chronic perphenazine treatment (4 mg/kg/day). Serum prolactin concentrations were 150 to 600 ng/ml in MTW9-P-bearing rats. MTW9-MtT does not regress after ovariectomy but does regress after surgical removal (resection) of MtT. Ovariectomy plus MtT resection leads to greater tumor regression than MtT resection alone.

MTW9-P does not regress when perphenazine administration is stopped but does regress after ovariectomy, whether or not rats are given perphenazine. Administration of estradiol (10 μg/day) to rats with complete ovariectomy-induced regression of MTW9-P results in regrowth of tumor.

These data suggest that MTW9-P may represent a clone of MTW9 with a lower requirement for prolactin.

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This investigation was supported by USPHS Research Grants CA 5215, CA 10064, CA 14194, and CA 02332 from the National Cancer Institute.

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