Pathogenesis of a rhabdomyosarcoma (undifferentiated type) in rats induced by a murine sarcoma virus (Moloney).

Murine sarcoma virus (Moloney) of mouse origin induced progressively growing local sarcomas in newborn OsborneMendel rats. Cell-free extracts prepared from the rat sar comas were oncogenic in newborn mice and in newborn, 2wpck-old, and 4-week-old Osborne-Mendel rats. The sarcomas were readily transplan table in Osborne-Mendel rats of the same age groups. Tumors in the early transplant generations tended to regress. However, tumors transplanted for 8 or more gen erations grew progressively. The primary or transplanted rat sarcomas, in contrast to the induced mouse sarcomas, consistently metastasized to the draining h-mph nodes and lungs. Whole cell transplants or cell-