Immunotherapy for cancer in cats and dogs.

Immunotherapy for Cats and Dogs with Cancer

Immunotherapy refers to a variety of treatments that stimulate the body's own immune system to either prevent or destroy
cancer. For many years, it was believed that the immune system was effective only in fighting infectious diseases caused
by invading agents such as bacteria and viruses. However, scientists have recently discovered that the immune system
also plays a role in protecting the body against development of cancer and in fighting existing cancer. These findings have
led to the design of novel immunotherapeutic strategies which, at this time, may be only available through clinical trials as
experimental therapies.

L-MTP-PE as immunotherapy for dogs with spleen hemangiosarcoma
Immunotherapy in combination with chemotherapy may be an additional option for dogs whose spleen hemangiosarcoma is
surgically removed. In a study with 32 dogs with Stage I/II spleen hemangiosarcoma (tumors that have not yet spread to
distant organs), all dogs received chemotherapy (doxorubicin and cyclophoshamide) after surgery but half the dogs also
received L-MTP-PE (a synthetic derivative of bacterial cell wall component) whereas the other half received placebo (an
inactive treatment to serve as a control). In this study, ~37% of dogs who received L-MTP-PE were disease-free after one
year compared to only 15% of dogs who did not receive L-MTP-PE. Dogs with Stage I disease had median disease-free
survival of 212 days (length of time after treatment during which half the pets had no sign of disease) and median overall
survival of 355 days (time from treatment at which half of the pets are still alive) compared to dogs with Stage II disease
(122 days for median disease-free survival and 148 days for median overall survival) (Vail et al, Clinical Cancer Research,
1995).

Cancer vaccines as therapy for cats and dogs with cancer
The goal of cancer vaccines can be twofold. First, the vaccine can be used to stimulate the pet's own immune system into
destroying its existing tumor, prevent cancer recurrence, or kill any cancer cells that may have been left behind by
previous treatments. Second, the vaccine can be used to prevent or delay the development of cancer in healthy pets.
Vaccines that are used to treat cancers take advantage of the fact that certain molecules on the surface of cancer cells
are either unique or more abundant than those found on healthy cells. These molecules can be used to stimulate the
immune system to make a specific immune response. Scientists hope that vaccines containing these cancer-specific
molecules will stimulate the pet's immune system to attack cancer cells without harming normal cells.

Vaccine for oral melanomas in dogs
In March 2007, the U.S Department of Agriculture granted a conditional approval of a DNA vaccine against c anine oral
melanoma. This was the first time that the U.S. government approved a therapeutic vaccine for the treatment of cancer in
either animals or humans. The vaccine was developed through a partnership between Merial, Memorial Sloan-Kettering
Cancer Center (MSKCC) and The Animal Medical Center (AMC) of New York. Clinical studies of the vaccine in dogs
showed significantly longer life spans even in dogs with advanced stages of melanoma. The vaccine is administered via a
new Canine Transdermal Device, which delivers the vaccine without the use of a needle. The approved protocol involves
administration of a dose of the vaccine every two weeks for four treatments, followed by a booster dose every six months.
The vaccine received full approval in 2010.

Monoclonal antibodies
Monoclonal antibodies are special types of proteins made in the laboratory that can locate and bind to molecules in the
body and on the surface of cancer cells. There are many kinds of monoclonal antibodies, each specific to a particular
molecule, and many of these have been approved for use in humans. There are currently no approved antibodies for the
treatment of cancer in cats and dogs.

Sources:

Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007.
Morrison Wallace B. Cancer in Dogs and Cats: Medical and Surgical Management. Baltimore: Williams&Wilkins, 1998.