An explanation for the proportion of carcinomas and sarcomas seen in chemically induced murine submaxillary gland tumors.

Pellets of 1 mg 9,10-dimethyl-1,3-benzanthracene (DMBA) were implanted into the submaxillary glands of 53 male C57BL/6J mice, and groups of mice were autopsied weekly or biweekly thereafter. Histologic evidence of tumor was noticed first at 12 weeks. From 16 weeks onwards, the submaxillary glands of all mice autopsied contained either carcinoma (three animals) or sarcoma (ten animals); 8/9 attempts to transplant these tumors in C57BL/6J mice were successful. Of the resulting eight tumor lines, two carcinomas and two fibrosarcomas were transplanted for over 30 months. Within the first few transplant generations, all four tumors showed an increase in growth rate and in histologic evidence of anaplasticity. For the particular tumors selected for study, the two carcinomas differed from the two sarcomas by growing more slowly, requiring more cells for tumor takes, and possessing a higher immunogenicity. These results may explain the types of tumors generated in submaxillary gland carcinogenesis. Carcinomas appear first, since they develop from the epithelial cells into which the carcinogen is implanted. Later, when fibroblasts wall off the carcinogen, fibroblasts are at risk for neoplastic conversion. Because of the more aggressive nature of the resultant fibrosarcoma cells, sarcomas may overgrow some early carcinomas.