Comparison of virus-positive and virus-negative cases of feline leukemia and lymphoma.

One hundred eighty-four cases of feline leukemia and lymphoma diagnosed in Boston from 1972 through 1976 were investigated. Fifty-eight % of these cases were lymphoma, and 42% were leukemia. Sixty-seven % of the cats had positive fluorescent antibody tests for circulating feline leukemia virus. The rest (33%) were virus negative. Clinically and epidemiologically, the virus-positive and virus-negative cases were remarkably similar except for their age at diagnosis. Virus-negative cats tended to be older (mean age at diagnosis, 4.9 years) as compared to virus-positive cats (3.5 years). For 22 cases of leukemia and lymphoma diagnosed after the age of 8 years, 15 were virus negative. The minimum mean induction period (time from first positive virus test to diagnosis of cancer) for 19 cats that were virus positive and healthy at their first test was 16.7 months (range, 2 to 41 months).