Is the 7,12-Dimethylbenz[a]anthracene-Induced Rat Mammary Tumor Model Suitable as a Preclinical Model to Study Mammary Tumor Malignancy?

To study the biological characteristics of 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary tumors in rats, 20 Sprague Dawley female rats received a single oral dose of 5 mg of this carcinogen. During the 35-week observation time 78 primary tumors were removed. While in most cases the primary tumor could be removed completely, 7 out of 20 animals eventually had to be sacrificed for inoperable local recurrence of the primary tumor. Notwithstanding, the long period of time given for tumor metastases to develop (mean time between tumor removal and termination was 18.5 weeks), tumor spread either to lungs or regional lymph nodes could not be established. This relatively benign behavior of the tumor was in contrast with the morphological characteristics of the tumor, which uniformly showed the features of adenocarcinomas. The difference in biological behavior between DMBA-induced mammary tumors in rats and malignant mammary tumors in humans suggests that as a model this system is of limited value for investigations of mechanisms of malignant behavior of human tumors.