| Abstract: | A cytogenetic study of 35 primary thymic lymphomas induced in rats by the Gross leukemia virus revealed the presence of widespread aneuploidies, ranging from cells with 35 chromosomes or less to triploid and tetraploid cells. Analysis by G banding revealed that chromosomes No. 1, 2, 9, 12, 18–20, X in females, and Y in males were lost preferentially; unidentified marker chromosomes of various morphology and length were present in a high percentage of aneuploid mitoses. Similar alterations were observed in preleukemic thymi from rats sacrificed 30 days after virus injection, when clinical or histologic signs of the disease had not yet appeared. In rats that were sacrificed 7 or 15 days after virus injection, chromosomal anomalies were much more limited, although significantly more abundant than in the controls. Rats that were free of tumor at 130–160 days after virus injection showed a regression of the chromosomal anomalies, suggesting that these are not irreversible and are not necessarily followed by the development of a lymphoma. |
