Studies on the role of C-type viruses in the development of epithelial tumors induced with DMBA.

Epithelial tumors were induced using 0.5 per cent solution of DMBA in two strains of mice--one infected with leukoviruses (Swiss mice), and the other is free of these viruses (hairless mice). Tumors from 15 mice of each strain were examined light- and electron-microscopically. Depending on the period of administration of the carcinogen, benign growths of the type of papilloma or keratoacanthoma were obtained, or malignant tumors. In the tumors in Swiss mice electron microscopy revealed a distinct increase in the numbers of viruses in comparison with surrounding skin and intact skin of healthy mice of this strain. In spite of certain histologic differences between tumors produced in Swiss and hairless mice, the results argue against a role of leukoviruses in the pathogenesis of experimentally induced epithelial tumors in mice.