Spontaneous tumors of NFS mice congenic for ecotropic murine leukemia virus induction loci.

NFS/N mice congenic for ecotropic murine leukemia virus (MuLV) induction loci from AKR and C58 mice ("NFS V-congenics") were evaluated for the development of spontaneous neoplasms in comparison to such development in virus-negative NFS/N mice. Congenic mice developed thymic lymphomas, whereas NFS/N did not. However, the frequency of thymic lymphomas was reduced, and the latent period for their development was prolonged in NFS V-congenics as compared to that in AKR/N or C58/Lw mice. In addition, the frequencies of nonthymic lymphomas and myelogenous leukemias were increased more than threefold in the congenics over NFS/N. The increased frequencies of hematopoietic neoplasms in congenic animals were related to early expression of high systemic levels of ecotropic MuLV.