Further tests for carcinogenesis using newborn mice: 2-naphthylamine, 2-naphthylhydroxylamine, 2-acetylaminofluorene and ethyl methane sulphonate

High incidence of rat mammary carcinoma by oral administration of ethyl methanesulphonate

Ethyl methanesulphonate (EMS), one of the alkylating agents, is known to be a potent mutagen. We tested EMS for its carcinogenicity in female rats by oral administration. EMS was dissolved in drinking tap water at a concentration of 10(-3) M and was given for the first 12 weeks. The subcutaneous tumors were noticed as early as 16 weeks after initiating the experiment. At the 32nd week, all the surviving rats produced tumors; the majority were multiple tumors in the neck, axillar and inguinal areas corresponding to bilateral mammary glands. Histologically, the prevailing feature of the tumors was infiltrating medullary adenocarcinoma consistent with carcinoma of mammary duct origin. Neither regional lymph node involvement nor distant metastases were shown, but intraductal spread of carcinoma was a marked finding during the 32-week period.

Possible two-stage transplacental liver carcinogenesis in C57BL/6 mice

A single SC injection of 2-acetylaminofluorene (AAF) was given to pregnant C57BL/6 mice on day 15 of gestation, and the offspring subsequently given twice-weekly injections of phorbol for 25 weeks. Control groups included: (1) untreated; (2) AAF-treated mothers (kept under observation for 18 months, as with all the other groups); (3) untreated offspring of untreated mothers; (4) untreated offspring of AAF-treated mothers, and (5) phorbol-treated offspring of untreated mothers. The incidence of hepatomas in the phorbol-treated offspring of AAF-injected mothers was 8/74 (11%), as compared with 2/80 (2.5%) in the untreated offspring of AAF-injected mothers. The AAF-injected mothers themselves developed 3/36 (8%) hepatomas; while all othe other control groups were free from liver tumours. The development of reticulum cell sarcomas, and of a few cases of lung adenomas, in the various groups, was presumably spontaneous. The results seem sufficiently encouraging, as a model for the study of systemic carcinogenesis, to warrant further attempts at two-stage transplacental carcinogenesis, using other potential initiators and promoters.

Carcinogenesis in rabbits injected at birth with 7,12-dimethylbenz(a)anthracene

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