What is Cancer?

Similar to humans, our pets are living and thriving longer due to advances in medicine and an emphasis on preventive care and nutrition. So, living a longer, quality life exposes our animals to diseases of aging, especially cancer. An estimated 6 million dogs and nearly 6 million cats will be diagnosed with cancer this year. In many of these animals, the malignancy will look and behave much as it would in humans, such as spreading to the same organs.

Cancer occurs when the body’s immune system cannot stop cells from replicating at an abnormally fast, disorderly pace and form a mass known as a tumor. Just as in humans, companion animal cancer is not caused by any single factor. While genetics and environmental factors can play a role in the disease’s development, other variables such as toxins, radiation and tumor viruses, as well as hormones can also be responsible for causing several types of cancer. And finally, suppressed or deficient immune systems can increase an animal’s risk of developing cancer.

Dogs are affected by more forms of cancer compared to other companion-animals. According to The Veterinary Cancer Society, cancer is the leading cause of death in 47% of dogs, especially dogs over age ten, and 32% of cats. Dogs get cancer at about the same rate as humans, while cats get fewer cancers. Some breeds or families of dogs have a higher incidence for developing cancer at an earlier age, but in most cases it’s a disease found in aging animals. There are nearly 100 types of animal cancer. Cancer in pets can be found in the skin, bones, breast, head & neck, lymph system, abdomen and testicles. Most common in cats is leukemia, while the most common cancers for dogs are lymphoma and mammary gland cancer.

Types of Cancer

Approximately 1/3 of all tumors in dogs are skin tumors, and up to 20% of those are mast cell tumors. The most common location to find mast cell tumors is the skin, followed by the spleen, liver, and bone marrow. Approximately half of all skin tumors are found on the body, another 40% on the limbs (most frequently the hind limbs), and the remainder on the head or neck. Approximately 11% occur in more than one location.

The list below highlights the most common types of cancer. Click here for a cancer reference sheet.

The Role of Comparative Oncology

The human-animal bond is stronger than you might think. In fact, the study of cancer in pet animals is shaping our understanding of cancers in people and leading to additional treatment options. According to a 2007 article by Philip J. Bergman, DVM, MS, PhD, DACVIM (Oncology) and Jeffrey Toll, VMD, DACVIM, the spontaneous cancers of pets treated by veterinary oncologists are similar to those arising in people. Dogs and humans are the only two species that naturally develop lethal prostate cancers. The type of breast cancer that affects dogs spreads to bones – just as it does in women. And the most frequent bone cancer of dogs, osteosarcoma, is the same cancer that strikes teenagers.

Based on these similarities between humans and companion animals, veterinary cancer research benefits both animals and humans with cancer. In fact, The National Cancer Institute’s Center for Cancer Research has instituted a critical Comparative Oncology Program where veterinary oncologists are using naturally occurring cancers in animals to better understand and treat cancer in humans.

What’s Next?

Emotions run high when we humans hear the word cancer. Should your veterinarian suspect cancer in your pet, the first step is to obtain a definitive diagnosis, develop a treatment plan along with your vet or veterinary specialist and prepare to be an advocate for your pet by arming yourself with information. Some other online sources of information include:

An estimated 6 million dogs and nearly 6 million cats will be diagnosed with cancer this year.