The phrase "leukemia virus" refers to a type of virus that can cause leukemia, which is a dangerous type of cancer that affects the blood cells in our body. Full definition
In fact, some cats with feline leukemia virus infection can live without major diseases for several years if they have good supportive care. (blog.nhvnaturalpetproducts.com)
There are many causes, but feline leukemia virus infection is the most common culprit. (www2.vet.cornell.edu)