Contrary to the name, Feline Leukemia is a virus, not a cancer. Feline Leukemia is spread through the saliva, making mutual grooming the most common cause of transmission, as well as bites. Nose-to-Nose contact, shared food and water bowls, as well as a shared litter box, may become sources of transmission as well. Little kittens may become infected while in the womb or when feasting on the milk of there mother.
Feline leukemia may present symptoms with loss of appetite, poor cat skin conditions, persistent fever, infections of skin and bladder, persistent diarrhea, and swollen lymph nodes. Make sure to get every new cat or kitten tested before introducing them to the house. Talk it over with your vet, and maybe consider vaccinating against this disease.