Dogs and cats get cancer just like humans. Cancer is one of the leading causes of disease in companion animals with 9% of all dogs diagnosed yearly with cancer and a similar number of cats. For comparison, every one out of two men will develop cancer and one out of every three women will develop cancer! However, some of the tumors found in companion animals are unique to their species whereas other types of tumors are similar between companion animals and humans.
The most common tumors of dogs and cats are lymphoma, mammary tumors, soft tissue sarcomas and mast cell tumors. Certain breeds of dogs are at higher risk of developing cancer such as Boxers, Golden Retrievers, Rottweilers and Bernese Mountain Dogs. However it is not possible to identify which dogs will develop cancer or definitively prevent cancer from developing in a dog.
Mammary cancer has been linked to not spaying (removing a dogs reproductive tract) in dogs and cats. Specifically, female dogs spayed early before their first estrus or heat cycle are seven times less likely to develop cancer than dogs spayed after their second or third heat cycle. European countries generally do not spay their pets however the incidence of mammary cancer in domestic pets within European countries is much higher than the US. Intact females are more likely to develop mammary cancer due to the influence of the sex hormones, estrogen and progesterone on cancer cell proliferation. Interestingly, mammary cancer occurs most frequently in cats and dogs but not in cows or horses suggesting that a carnivorous diet may have higher levels of environmental carcinogens or contain harmful hormones.
Lymphoma is a cancer of the white blood cells or lymphocytes in which the white blood cells proliferate at a higher rate than normal. Golden Retrievers are considered to be a breed with a higher risk of developing lymphoma however older dogs of any age and breed can be affected. Lymphoma develops where lymphoid tissue is normally present mainly the lymph nodes, spleen, liver, gastrointestinal tract and bone marrow. Lymphoma that affects the lymph nodes is the most common form with involvement of the gastrointestinal tract the second most common form.
Cancer management is centered on the common armament of surgery, radiation and chemotherapy with immunotherapies available for very few cancers such as melanoma. The type of treatment used depends on the tumor type, the extent to which the tumor has spread locally and systemically as well as the animal’s quality of life during and after treatment. However, treatment options for cancer in animals is very limited and sadly outdated.
New treatment options for cancer management are beginning to appear thanks to concerted efforts to conduct well ran clinical trials in animals. In 2009, the FDA approved the first drug specifically for canine cancer, Palladia to treat mast cell tumors that develop on the skin. Advanced treatment options such as CyberKnife Robotic Radiosurgery System are also making their way into veterinary clinics. This treatment delivers beams of high dose radiation to tumors with extreme accuracy removing the need for invasive surgery and enables veterinarians to treat tumors that are not easily accessible and treat patients that may not be good surgery candidates.
Until a cure for cancer is found, the treatment and management of cancer in animals will continue to improve. Accordingly our knowledge of the disease and its causes will continue to expand. Comparative oncology programs and clinical trials in companion animals also provide opportunities to translate what is learned from treating cancer in dogs to cancer in humans.