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Studies of the Kinetics of Growth and Regression of 7,12-Dimethylbenz()anthracene-induced Mammary Adenocarcinoma in Sprague-Dawley Rats¹

Kettering-Meyer Laboratory, Southern Research Institute,² Birmingham, Albama 35205

The cell cycle of 7,12-dimethylbenz()anthracene-induced mammary adenocarcinoma in female Sprague-Dawley rats has been studied by autoradiographic techniques and the lengths of the cell cycle and its phases (hr) are: T_C, about 20; T_S, 8.5; T_G1, about 11.5; T_G2, 1.0; T_M, about 1.0. The thymidine index is generally low (<10) in growing tumors and is sharply reduced in tumors regressing after ovariectomy. The thymidine index remains low during stasis of growth in tumors regressed by ovariectomy and increases in spontaneously recurring tumors. Administration of estradiol and progesterone to ovariectomized animals with regressed or static tumors results in an approximately 10-fold increase in thymidine index.

¹ This investigation was supported in part by the Endocrine Evaluation Branch, General Laboratories and Clinics, National Cancer Institute, USPHS, under Contract PH43-66-71 and in part by Chemotherapy, National Cancer Institute, NIH, under Contract PH43-66-29.

² Affiliated with the Sloan-Kettering Institute for Cancer Research, New York, N. Y.

Received 6/16/69. Accepted 8/27/69.