Topographical distribution of dimethylbenz(a)anthracene-induced rat mammary tumors.

Intravenous administration of dimethylbenz(a)anthracene (DMBA) in the rat induces multiple mammary tumors. The nodules, benign or malignant, develop preferentially in the thoracic part of the milk line. Actinomycin D interferes with the carcinogenic action of DMBA, but it does not alter the regional distribution of the tumors formed. Evaluation of experimental data, using this tumor model, should take tumor topography into consideration.