Lymphosarcoma is the most commonly diagnosed cancer in ferrets. It occurs in both old and very young ferrets. Lymphosarcoma affects the lymph nodes and other lymphatic tissue, for instance in the spleen and liver. It may or may not cause leukemia. Leukemia means that malignant white blood cells can be found in blood samples. Lymphosarcoma is common in other animals and in human beings.

Ferrets with lymphosarcoma may suddenly seem lethargic and fail to be as active and playful as usual. They may have recurrent respiratory infections, lose weight, and may have poor appetites. Often an enlarged spleen or lymph node can be felt from the outside of the animal. Your veterinarian will take a biopsy or remove a whole lymph node to decide whether the enlargement has been caused by cancer.

Lymphosarcoma is treatable in some animals. Chemotherapy may be successful, but it is a lengthy and costly endeavour. Large tumors, for instance in the spleen, may be surgically removed, even if chemotherapy is to be used. There is no guarantee that either surgery or chemotherapy will cure the disease, but ferrets are good patients and chemotherapy has fewer side effects in them than it does in people. Many owners feel it is well worth trying to save their pets, and many ferrets survive and live normal lifespans afterward.

In some animals, leukemia is associated with certain viral infections. Feline leukemia is caused by a virus that is transmitted from the mother cat to her kittens, and from cat to cat. Bovine leukemia virus affects cattle and is mainly transmitted from cow to calf. Tests can detect the feline and bovine viruses in cats and cattle respectively, but there are no such tests to detect similar viruses in ferrets or in people with lymphosarcoma. It is likely that a virus causes lymphosarcoma in ferrets, and is passed from jills to their kits and from one pet to another. It is likely that similar but not identical viruses cause lymphosarcoma in different kinds of animals and in people.

Occasionally, Aleutian Disease Virus (ADV) causes a disease in ferrets that may appear similar to lymphosarcoma. A blood test will identify animals that have ADV, but most ferrets that test positive never show signs of illness. Blood tests, biopsies, and/or exploratory surgery may be necessary to distinguish Aleutian Disease from lymphosarcoma in ferrets.