It started out small—a tiny sore on a previously concealed lump near her lower abdomen. At twenty-two years old, our beloved tiger Raja was showing signs of breast cancer.
In recent years, the campaign against breast cancer in women has been widely publicized, the iconic pink ribbon appearing on t-shirts, key rings, water bottles, and other accessories which are sold to increase awareness of the disease and raise funds for research. Breast cancer in animals, however, is not nearly as well-recognized.
Little is known about the occurrence of breast cancer in the wild, as it is difficult to study such diseases in a natural setting. Wild animals typically live much shorter lives than those in captivity and are likely to succumb to injuries, starvation, or some other form of disease before the cancer would have a chance to manifest itself. Additionally, in order to avoid attacks by predators or competitors, wild animals—particularly those of an elusive nature like the cat—will often hide the symptoms of an illness for as long as possible, and the remains, if found, are often in such poor condition that it would be near impossible for an accurate necropsy to be performed. Because of this, most of what we know about breast cancer in animals comes from studying the behavior of the disease in zoo animals and pets.
A 2012 study surveying over a thousand necropsied zoo mammals found one hundred and eight of the deaths to be cancer-related; mammary tumors were the most common form of cancer, accounting for 12% of the cases. In general, breast cancer appears to be more prevalent in carnivores than herbivores, likely due, in part, to the tendency of toxins, such as carcinogens, to build up in the tissues of animals higher on the food chain.
Breast cancer is the third most common type of cancer in domestic felines, responsible for 17% of all tumors in female cats. Eighty to ninety percent of these mammary tumors are malignant (cancerous), and most cats with the disease are lucky to survive a year after diagnosis, as the tumors are aggressive and tend to grow back quickly after removal and spread to other parts of the body, such as the lungs and lymph glands. The frequency and severity of the disease appear to be similarly high in captive big cats; a study at the Knoxville Zoo documenting cases of cancer in their cat collection over a period of twenty-four years noted that breast cancer appeared in more than a fourth of the animals diagnosed. Six of the seven cases of breast cancer were found in tigers, and all six tigers’ deaths were attributed to the disease. However, it is difficult to say whether such a high rate of cancer is natural for wild felids, as many of the cats in the study (including the six tigers who died from mammary tumors) were exposed to a contraceptive drug that is now known to cause breast cancer.
In the wild, lions and tigers usually breed every other year, but in captive situations, it may be necessary to prevent breeding on such a regular basis. Although spaying (removing the uterus and ovaries) is an option, if the animal has good genetics, zookeepers may want to retain the possibility of breeding her in the future as part of the Species Survival Plan, so alternative forms of birth control are often required. For many years, the drug of choice was a progestin-containing compound known as MGA. It is now widely recognized, however, that prolonged exposure to the hormone progesterone—whether by artificial means or by repeatedly going into heat without being bred—can greatly increase a cat’s chance of getting breast cancer. Studies on housecats have shown that females spayed before they are six months old are over 90% less likely to develop breast cancer later in life; spaying a cat later in life, though less effective, still reduces the risk by at least 40%. In contrast, domestic cats exposed to progestin—which is contained in drugs that are used to treat skin disorders and behavioral problems as well as contraceptives—are almost three times more likely to develop mammary tumors than those untreated, and, in some cases, even male cats exposed to the hormone have developed breast cancer.
Though we now have a fairly good understanding of the behavior of mammary tumors in domestics, because breast cancer is still poorly understood in many wild animals, a comprehensive study of the disease across a wide range of species is necessary. The Association of Zoos and Aquariums’ (AZA) Reproductive Health Surveillance Program aims to achieve that goal. By comparing the reproductive organs and other affected tissues of animals with mammary tumors to those without cancer, the AZA hopes to gain a better understanding of how breast cancer behaves in wild species and the side effects of various contraceptive drugs.
On January 21, 2014, Raja lost her battle with breast cancer. In the hopes of preventing other animals from enduring the same sort of suffering, the staff at Crown Ridge decided to donate her body to the Reproductive Health Surveillance Program for research purposes. If you would like to contribute to this research and help raise awareness of feline breast cancer, please consider purchasing one of our “Fight Like a Tiger” t-shirts in memory of Raja. All proceeds will benefit the Reproductive Health Surveillance Program.