I'm going to try to explain this
"Leukemia" means cancer of the white blood cells. This was the first disease associated with the feline leukemia virus (FeLV) and, thus, the source of its name. We often use the term "leukemia" rather loosely to include all of the diseases associated with the virus, even though most are not cancers of the blood. This virus causes many other fatal diseases, in addition to leukemia.
Feline leukemia virus is classed as a retrovirus. The retroviruses are of particular importance because they have the ability to integrate into the genetic material, or DNA, of the host. For this reason, some call the retroviruses “the ultimate genetic parasites.” There are three subtypes of the virus and the diseases caused are dependent upon the particular subtype involved. The feline immunodeficiency virus, or feline AIDS virus, is another feline retrovirus.
There are three major disease categories associated with the FeLV:
1) Leukemia is a cancer of the white blood cells.
2) Lymphosarcoma (also called Lymphoma) is a cancer of many different organs but it begins in lymphoid tissue, such as a lymph node. Almost any tissue may be affected; organs commonly involved include lymph nodes, intestinal tract, kidneys, liver, spinal cord, brain, bone marrow and blood. In young cats, lymphoma often manifests as a mass within in the thoracic cavity; this is called “mediastinal lymphoma.”
3) The Non-Cancerous Diseases include a variety of somewhat unrelated diseases. Anemia, abortion, arthritis, and immune suppression are examples. When the immune system is suppressed, the cat becomes susceptible to many diseases it would ordinarily resist and mild diseases, such as respiratory infections, may become fatal.TreatmentLeukemia.
Some forms of leukemia (blood cancer) are unresponsive to all available forms of cancer treatment. Other types of leukemias may respond to chemotherapy, though most of these have an average survival time of less than one year. Because the virus is not affected by treatment, the cat will always remain infected with FeLV. Also, relapse of leukemia is possible (and expected). These factors cause us to recommend treatment of leukemia in very few situations.Lymphosarcoma.
Lymphosarcoma is treatable, but not curable. Research has shown that cats with lymphoma who are FeLV-positive do not respond to treatment as well as FeLV-negative cats.Secondary infections.
Depending upon the type of infection involved and the general state of the cat’s health, the prognosis may range from favorable to guarded. For example, bacterial infections may respond well to antibiotic therapy. Other types of infections, such as certain fungal infections, may not respond well because of the FeLV-induced weakness of the cat’s immune system.The healthy FeLV-positive cat.
Healthy infected cats may remain apparently unaffected by the virus for several years. With good supportive care and prompt attention to all potential medical problems, these cats may live for a number of years. Bear in mind that these cats should be considered infectious and potentially dangerous to other cats.
The prognosis is dependent upon many factors. In general, 80% of all persistently positive cats (IFA positive) succumb within three years, most of these deaths occurring within the first six months of detection. The cat who is transiently positive may expect a normal lifespan, or may become ill if latent virus in the body is reactivated.
The virus can be reactivated by many internal and external stressors such as changes in the environment, steriods, illness, fatigue etc. If this occurs, it is like hitting the reset button and the cellular changes can begin the transition into cancer somewhere in the body again.
Thanks for the good explanation, Angie.