Lack of growth of a pregnancy-dependent mouse mammary tumor (TPDMT-4) in the absence of pituitary hormones.

Mammary tumors of line TPDMT-4, established in DDD mice, were characterized by growth during pregnancy and regression after parturition; this resulted in higher growth peaks in subsequent pregnancies in breeders and no growth in virgins. The effect of hypophysectomy on tumor growth in mice given 17beta-estradiol (E) and progesterone (P) or deoxycorticosterone acetate (DCA) was investigated. Growth of cancers occurred in E+P- and E+DCA-treated virgins, but not in cholesterol-treated virgins. Tumors did not grow to palpable sizes in cholesterol-, E+P-, and E+DCA-treated hypophysectomized virgins; this indicated that pituitary hormones were essential for tumor growth. Impalpable cholesterol-treated, 5 of 10 E+P-treated, and 3 of 6 E+DCA-treated hypophysectomized animals. The neoplasms showed ductal and tubular structures that were lined by a single layer of well-differentiated buoidal epithelium, which suggested that the tumor line might be derived from ductal cells.