Non-random chromosome changes in a herpes-virus-transformed Syrian hamster cell line and its metastatic derivatives.

A primary subcutaneous tumour of low spontaneous metastatic capacity, produced after inoculation of Herpes-virus hominis type-2-transformed hamster fibroblasts (parent line) and two in vivo derived highly metastatic lung deposits (Met A and Met B) were karyotyped and compared after trypsin G-banding. The parent line was cytogenetically heterogeneous with a modal chromosome number of 74. However, a number of cells were of a higher ploidy level. A large variation in both numerical and structural abnormalities was observed, the chromosome rearrangements were often complex and unstable, but all the cells contained a theme of common marker chromosomes. Met A and Met B were near diploid (mean chromosome numbers 42 and 44 respectively) with a low level of tetraploid cells. They shared many chromosome rearrangements but could be readily distinguished by an additional translocation unique to Met A. Cytogenetic homogeneity within and between metastases suggested that they were of monoclonal origin and had been derived from a karyotypically similar subpopulation within the parent tumour. We were unable to detect such cells in the parent line; thus, their numbers within the parent tumour were likely to be low. Metastasis, therefore, has been highly selective, depending on the particular phenotypic properties of Met A and Met B. All cells of the parent and metastatic lines have homogeneously staining regions (HSR) and abnormalities of chromosomes 15 (C15) which may be important in tumorigenesis. In addition, Met A and Met B cells have a number of chromosome rearrangements [translocations, deletions and a double minute chromosome (DM)] not present in the parent cells. They are retained at a high frequency in the cells of Met A and Met B and thus it seems likely that the metastatic phenotype is associated with one or more of these chromosome aberrations.