Home » Pet Health » Feline Infections and Viruses » How Does FIV Infection Increase Cancer Risk?


Feline immunodeficiency virus (FIV) is one of the most common causes of infectious diseases in cats. Its frequency varies depending on geography but is more common in outdoor cats. Therefore, rates of FIV are higher in regions where the prevalence of domesticated indoor cats is lower. While FIV is not directly cancer-causing, there are a few ways the virus can lead to cancer development:

    1. Uncontrolled cell growth. Because the virus enters the immune cells to replicate, there is a possibility some mechanism within the cells might be disturbed, leading to unchecked growth of the cell. This uncontrolled growth can result in cancer.
    1. Weak immune system. FIV is known for its prolonged ability to weaken the cat’s immune system. A compromised immune system can significantly increase a cat’s susceptibility to developing cancers.
    1. Overactive immune system. Viruses can also cause chronic inflammation and increased immune system activation, especially of the antibody-producing immune cells called B cells. Studies have shown that increased B-cell activation can lead to cancer development.

Blood-based cancers, such as lymphoma, are the most common cancers linked to FIV. The infection can also increase the risk of other cancers such as squamous cell carcinoma (SCC), fibrosarcoma, and carcinoma. SCC can appear as tumors on the skin or mouth of the cat, but oral SCC is the most common form associated with FIV. Fibrosarcoma is another common oral cancer present in cats. Carcinoma, in contrast, is most commonly found on mammary glands in cats with FIV.

Lymphoma, the primary cancer type associated with FIV, is a cancer of immune cells and lymph node tissue, which the virus infects. Cats that develop lymphoma after FIV infection begin to typically grow tumors 2 to 6 years after the initial FIV diagnosis, though cats of any age and breed can be affected. Some of the most common tumor sites for FIV-positive cats with lymphoma include the lymph nodes, nasal cavities, kidneys, intestines, and brain. If the lymphoma is only in the bone marrow, it is called leukemia.

Cancer treatment

Treatment for feline cancer includes conventional cancer therapies, including surgery, radiation, and chemotherapy. Radiation is the typical therapy if the cancer is only in one area of the body while adding chemotherapy is more beneficial for cancers that have spread. The usual treatment for oral SSC, fibrosarcoma, and carcinoma is the surgical removal of the tumor and affected tissue. Unfortunately, these cancers are considered aggressive and can move to other body parts if not caught early enough. It is important, therefore, to regularly examine your pet for signs of oral and skin cancers, especially if diagnosed with FIV. Thankfully, cancerous lymphomas are very responsive to chemotherapy. Some owners may be hesitant to give chemotherapy and radiation to their FIV-positive cats because FIV is known to suppress the immune system. However, many researchers believe FIV does not disqualify a cat from chemotherapy in the right situations. Talk to your vet about appropriate treatments if your cat is diagnosed with lymphoma.


Despite the high incidence of FIV, it tends to occur more frequently in cats that spend most of their time outside. Therefore, the best way to protect your pet from getting the virus is by keeping them inside and, if they interact with other cats, ensuring those other animals are FIV-negative. By taking these measures, your cat will be at a lower risk of developing FIV-related cancer. But, if you suspect your cat has been exposed to the virus, speak to your vet so they can determine if your cat is FIV-positive and discuss the next steps.

The Pet Cancer Foundation’s Website Editorial team is comprised of veterinarians, veterinary oncologists, and veterinary technicians, as well as scientific writers and editors who have attained their PhD’s in the life sciences, along with general editors and research assistants. All content found in this section goes through an extensive process with multiple review stages, to ensure this extended resource provides pet families with the most up-to-date information publicly available.

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Last Updated: October 13, 2022

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The following sources were referenced to write the content on this page:

Hartmann, K 2012, ‘Clinical aspects of feline retroviruses: a review’, Viruses, vol. 4, no. 11, pp. 2684-2710.

Henry, C & Higginbotham, ML 2009, Cancer Management in Small Animal Practice-E-Book, Elsevier Health Sciences.

Hosie, MJ & Lutz, H 2022, ‘Feline immunodeficiency virus’, Schalm’s Veterinary Hematology, pp.424-430.

Kaye, S, Wang, W, Miller, C, McLuckie, A, Beatty, JA, Grant, CK, VandeWoude, S & Bielefeldt-Ohmann, H 2016, ‘Role of feline immunodeficiency virus in lymphomagenesis–going alone or colluding?’, ILAR J, vol. 57, no. 1, pp. 24-33.

Magden, E, Quackenbush, SL & VandeWoude, S 2011, ‘FIV associated neoplasms–a mini-review’, Vet Immunol Immunopathol, vol. 143, no. 3-4, pp. 227-34.

The Pet Cancer Foundation’s medical resource for pet owners is protected by copyright.

For reprint requests, please see our Content Usage Policy.