Cytogenetic changes in Sprague-Dawley rat lymphomas in the course of in vivo passages.

Changes in the karyotype in three spontaneous Sprague-Dawley rat lymphomas (SD7/95, SD8/96, SD9/96) have been studied in the course of in vivo passages. In individual lymphomas karyological findings of primary disease from lymph nodes were compared with changes found in the 1st and 10th passages of the lymphoma and bone marrow samples. Chromosome studies were performed on direct preparations using the G-banding technique. Chromosome counts of all specimens studied were near diploidy, the majority of metaphase cells being pseudodiploid. In later passages of two lymphomas, the tendency in selection to hyperdiploid karyotype, particularly in bone marrow was observed. The examination revealed an increased percentage of breaks in lymph node cells of primary disease and the existence of nonrandom change, derivative chromosome 11, which occurred in structural variability in all three lymphomas studied. The aberration involving chromosome 11 was evaluated as the addition of unknown material at chromosome band 11q11 or as a duplication or triplication of segment 11q12-q23. If this structural aberration was not found, the excessive derivative chromosome 11 or translocation t(11;13) was proved to be present. Further, rearrangements of chromosomes 13 and 7 were nonrandom chromosome abnormalities revealed in later passages of the lymphomas. The results are in accordance with our previous observations in 14 cases of SD lymphomas that showed nonrandom occurrence of rearrangements concerning chromosome 11 and also relatively frequent translocation involving chromosome 13.