Chromosome abnormalities and oncogenesis in cat leukemias

Chromosome abnormalities are found in feline leukemia virus (FeLV) infected tumor cells as well as in tumor cells free of the virus. On the other hand, normal feline cells infected with the virus do not show chromosomal abnormalities. Here I ask whether chromosome abnormalities and viruses can each cause or play a role in the causation of tumors. Cytogenetic analyses on three cell lines derived from tumors in the domestic cat (Felis catus), two of thymic origin and one of multicentric lymphoma origin, have been carried out in an attempt to determine whether the FeLV virus was associated with chromosomal abnormalities in these tumors. One thymic tumor and the multicentric lymphoma were FeLV-infected. The other thymic tumor cell line was FeLV-free. The normal diploid number in domestic cat is 38. All three cell lines had numerical chromosome abnormalities with modal numbers of 37, 38 (pseudodiploid), and 39 respectively. All three cell lines also had structural (marker) chromosome abnormalities that were consistent within cell lines. Three of the markers found in the virus-free cell line (U markers) were shared with either of the virus-positive cell lines. The two FeLV-positive cell lines did not have U markers in common. Since both the virus-infected and the virus-free cell lines have chromosomal abnormalities, this suggests that these abnormalities may be an important factor in oncogenesis. Although the FeLV virus may cause chromosome abnormalities, it could not be considered to be the only causative agent of the abnormalities observed.