Murine leukemia virus in chemically-induced sarcomas as detected by XC plaque formation

To detect whether methylcholanthrene induced murine sarcomas contain endogenous murine leukemia viruses, direct XC syncytium assays were performed over short term tumor cultures. Out of 31 sarcomas, 13 (42%) induced more than 4 plaques per flask, while no such activity was found in 39 control spleen samples. It is postulated that the positive tests are related to an increase in the titer of endogenous B-tropic virus, probably as a result rather than as a cause of tumor induction by chemicals.