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Carcinogen-induced Mammary Tumors from Preneoplastic Nodule Outgrowths in BALB/c Mice¹

Department of Zoology and Its Cancer Research Genetics Laboratory, University of California, Berkeley, California 94720

The oncogenic effect of two chemical carcinogens, 7,12-dimethylbenz(a)anthracene and urethan, and of -irradiation was tested on 2 of the D series of BALB/c nodule outgrowth lines, D1 and D2. All 3 agents increased the tumor-producting capabilities of nodule outgrowth line D1, and -irradiation also increased the tumor-producing capabilities of nodule outgrowth line D2. The two chemical carcinogens were not tested on D2. The tumor-producing capabilities of the nodule outgrowth lines were dependent both on the particular carcinogen tested and on the nodule outgrowth line used. Nodule outgrowth line D1 treated with urethan or with 7,12-dimethylbenz(a)anthracene produced 76% and 64% tumors, respectively, whereas irradiated outgrowth line D1 produced only 22% tumors. Untreated D1 outgrowth produced only 4% tumors. On the other hand, irradiated outgrowth line D2 produced 61% tumors, whereas untreated D2 outgrowths produced 14% tumors.

Blood from carcinogen-treated mice and cell-free extracts of tumors arising in carcinogen-treated outgrowths were assayed for the presence of mammary tumor virus activity by the noduligenic assay. In addition, thin sections of carcinogen-treated outgrowths and tumors derived from carcinogen-treated outgrowths were examined under the electron microscope for the presence of A and B particles. Neither virus particles nor evidence of mammary tumor virus activity were encountered.

¹ Supported by USPHS Grants CA 5045 and CA 05388 from the National Cancer Institute.

² Recipient of NIH Predoctoral Fellowship 4-F01-GM-38, 779-02. Present address: Department of Anatomy, Baylor College of Medicine, Houston, Texas 77025.

Received 8/ 7/69. Accepted 10/ 9/69.