Development and characterization of mouse hyperplastic mammary outgrowth lines from BALB/cfC3H hyperplastic alveolar nodules.

Five hyperplastic outgrowth lines were developed by serial transplantation of hyperplastic alveolar nodules from BALB/cfC3H mice into BALB/c hosts. The lines were used to study the biology, morphology, and virology of premalignant tissue originating in mouse mammary tumor virus (MuMTV)-positive animals. The five lines differed with respect to tumor potential and growth characteristics, corroborating the previous evidence that MuMTV-positive hyperplastic alveolar nodules are biologically heterogeneous. Subgross and microscopic examination of outgrowths and tumors revealed that each line had unique morphological characteristics. The presence of atypical lobules within the hyperplastic outgrowth appeared to be correlated with tumor risk, and a morphological continuum of atypical lesions ending in overt cancer was suggested. Viral expression was detected by nucleic acid hybridization and immunoperoxidase staining for MuMTV structural antigens. While the MuMTV RNA in certain tissues appeared to vary qualitatively with tumor potential of the outgrowth line, no correlation between viral antigens detected by immunoperoxidase staining and tumor potential was observed.