2016-10-19 / Columnists
Pets, Pets, Pets
October is Breast Cancer Awareness Month. Dogs can develop breast (mammary) cancer too. Actually, the disease is quite common. When the “One Health” movement emerged linking findings in human and veterinary medicine, scientists started taking a closer look at canine breast cancer because veterinary discoveries have the potential to help both dogs and people.
The frequency of mammary cancer in different species varies tremendously. The dog is affected more often than other domestic species, with a prevalence about three times that in women. Meanwhile, mammary tumors are rare in cows, mares, goats, ewes and sows. The Merck Veterinary Manual reports there are differences in mammary tumors in dogs and cats. Approximately 45 percent of mammary tumors are malignant in dogs, whereas about 90 percent are malignant in cats.
The most common type of tumor in female dogs is a mammary tumor, especially in unspayed females between five and 10 years old. It is rare for male dogs to develop mammary tumors but, if affected their prognosis is usually not good because this type of malignancy is quite aggressive.
Reducing hormone levels by spaying a dog before her first heat cycle was longtime veterinary advice. Dogs spayed before their first heat have only a .5 percent risk (practically no chance) of developing mammary cancer. The risk increases to eight percent when spayed after the second heat. By 2.5 years of age spaying offers no decreased risk benefit. However, new research about possible effects of early spaying complicate the decision because some studies suggest the absence of ovarian hormones may predispose dogs to a greater risk of joint disease and other cancer types.
People who compete in canine performance events like agility are paying close attention to new evidence connecting early spays and joint disease. It is going to take more time and more research to determine the best time to spay.
Obesity may be a factor. In one study, the risk of mammary carcinoma among spayed dogs was reduced by 40 percent in dogs that had been thin at nine to 12 months of age. However, the risk did not decrease, in intact dogs of the same age. In another study, dogs with a higher intake of red meat in their diet were at higher risk for developing mammary cancer.
Genetics plays a part too. A 2013 study in Norway led to the identification of genetic changes associated with canine mammary tumors. Since the 1960s research has compared frequency of this cancer in different breeds. Breast cancer seems more common in English Springer Spaniels, Toy and Miniature poodles, Pointers and German Shepherds.
A dog normally has two rows of five mammary glands each with their own nipple on the right and left side of her abdomen. Although mammary cancer does occur in all of the glands, it occurs most frequently in the fourth and fifth glands. In half of the cases more than one growth is found.
You can examine your dog when rubbing her belly. The lumps usually feel like large pieces of gravel under the skin, very hard and difficult to move, and they grow quickly, doubling in size monthly. Malignant growths can cause bleeding and ulceration. But any lump you discover should be promptly brought to your veterinarian’s attention.
The best way to diagnose breast cancer is with a surgical biopsy of the mass. In dogs with large masses, it may be possible to obtain a fine needle aspirate of the tumor. X-rays can search for metastasis. Surgical removal is recommended unless the patient is very old. If a surgery is done early, this cancer can be eliminated in over 50% of the cases. Sometimes only the mass itself will be removed. Other times, considering how the cancer spreads, the mass plus the rest of the mammary tissue and lymph nodes that drain the gland will be removed.
The canine operation tends to have an easier recovery than a radical mastectomy in women where underlying muscle tissue is affected too. In the dog, all of the breast tissue and related lymph nodes are outside of the muscle layer. Although this is major surgery, suture removal usually occurs in ten to 14 days with the dog normal activity resuming at that point. Many vets will spay the dog (unless quite old) at the same time as tumor to decrease the chance of reoccurrences. Neither chemotherapy nor radiation has proven effective thus far with canine mammary masses.
The University of Pennsylvania Veterinary School has a unique program which saves shelter dogs with mammary cancer, advances knowledge about the disease for pets and people and pairs homeless dogs with people willing to care for them. The Canine Mammary Tumor Program at the Ryan Veterinary Hospital in Philadelphia is based on the premise that female dogs entering shelters tend to be unspayed, and because of this many develop mammary tumors. The older females are most vulnerable because if they need complex medical attention, their chances of adoption are slim. They are more likely to be euthanized. Entrance into the program gets them the care they need, and makes them more adoptable.
In addition, dogs are excellent models to study because they have five pairs of mammary glands. The vets can be treating several tumors at different stages of the disease. Because of the similarities between this cancer in dogs and humans, the results can have application to human breast cancer research. Close to 200 dogs have gone through the program thus far, and except for those too ill for surgery, the rest have been placed in loving homes. They remain in the program for follow-up visits. How do you spell “win/win”?
For Adoption: “Gretchen” is an eight-year-old, purebred German Shorthaired Pointer. Her 95-year-old owner recently passed away. She is affectionate, active, adorable and needs a loving home, preferably with a Pointer person. Call 631-671-2588. “Krissy”6-387 represents all the cute kittens at Babylon Shelter (631-643- 9270) Lamar St., W. Babylon.