Dr. Marthina Greer finds it heartbreaking to see a dog die from a preventable disease. She aims to educate pet owners about the fact that mammary gland cancer — the veterinary equivalent of breast cancer — can be avoided by spaying pets when they’re young. 

Greer’s practice specializes in canine reproduction, so many of her clients have intact bitches. She rarely loses a breeding dog to mammary gland cancer because in her experience, breeders monitor their dogs for masses and have them removed. It's the average pet owner who's often uneducated about the connection between mammary gland cancer in female dogs and sterlization, she said.

That's because sterlization is widely promoted as a means for controlling pet populations — not preventing cancer.

“The shelters and others have done a great job of teaching clients and pet owners about population control,” Greer said, “but breast cancer has been left as a poor cousin of a reason to spay your bitch.”

Greer sees approximately one new case of canine mammary gland cancer a week in her Lomira, Wis., practice. “The ones we lose are usually bitches who were not spayed but were not bred and were never intended to be bred,” she said. In 30 years of practice, she has encountered four cases of inflammatory mammary carcinoma, what she calls “the worst of the worst," alluding to the cancer's aggressive nature.

To spread the word about cancer-related benefits of sterlization, Greer believes some terminology needs improvement. "Why do we call it mammary tumors? No wonder the clients don't know what we're are talking about," she muses.

She'd rather have the condition referred to as breast cancer, a more common reference. 

What causes mammary gland cancer is unknown, though hormones are believed to play a role in its development. Signs of cancer include firm nodules in the tissue around the nipples, ulcerated skin, swelling and inflammation as well as discharge in some cases.

Cats are not immune to mammary gland cancer, though statistics of incidence vary depending on the study. Generally speaking, mammary gland cancer occurs less often in cats than in dogs. However, studies show that 80 to 90 percent of the mammary tumors in cats are malignant. The malignancy rate for mammary tumors in dogs is 50 percent.

“Mammary gland cancer is certainly in the top three (most common cancers in cats)," said Dr. Ruthann Chun, a board-certified oncologist and head of clinical oncology at the University of Wisconsin School of Veterinary Medicine. “I think it is fair to say that we see more dogs with mammary cancer, but whether that actually means it is more common in dogs is another question that I can't answer. For sure, when we see a mammary tumor in cats, it is much more likely to be malignant.”

Incidence is a hard to pin down because most research papers exploring the topic were written in the 1960s, notes Dr. Corey Saba, a board-certified oncologist working at the University of Georgia College of Veterinary Medicine.

"It has been published (in the 1960s) that mammary tumors are 'at least the third most common tumor in cats,' but I can't say that's been my clinical experience," wrote Saba in an email interview with the VIN News Service. "I also don't know that mammary cancer is any more or less common in cats versus dogs. The main predictor of mammary gland tumor (MGT) development seems to be timing of spay, and because most pets are spayed as kittens and puppies, we really don't see a lot of mammary cancer in either species. In fact, a lot of the recent studies about MGT have come out of Europe and South America because spaying is less common in those countries."

Saba characterized her typical mammary gland cancer patient as a dog or cat spayed "later in life" after at least one heat cycle. However, spaying a dog or cat at a young age does not guarantee future good health, even if it works to ward off mammary gland cancer.

There are health benefits to leaving pets intact, and Greer notes that spaying has drawbacks. For example, spaying a dog that's less than a year old is believed to increase its risk for developing osteosarcoma, splenic hemangiosarcoma and hypothyroidism. Still, spaying before the first heat cycle protects nearly all dogs from mammary gland cancer, Greer said.

“I think spaying needs to be discussed with all clients — risks and benefits. In contrast to humans, mammary tumors in dogs are nearly 100-percent preventable if owners would take one simple step: to spay their female dogs prior to age 2 or younger,” Greer said. “We all know that spaying (ovariohysterectomy or ovariectomy) prevents heat cycles and pregnancy. What we have not always done as well as we should have as veterinarians is to educate our clients that spaying under age 2 prevents most mammary tumors." 

Saba recommends spaying cats between 6 months and 1 year of age. Research shows that cats spayed after age 1 are at greater risk for developing mammary gland cancer than felines spayed before their first year.

Greer is considering how she might educate the public by way of a national campaign. Right now, she's reaching out to her clients with a message that sterilization is a cancer preventative. 

Because October is National Breast Cancer Awareness Month, every pet spayed in Greer's clinic will go home wearing a pink ribbon bandanna that resembles the pink ribbons promoting knowledge of disease in humans and early detection efforts.

Given that women are taught to conduct monthly breast self-examinations, Greer wants to piggyback onto that idea by reminding women to check their female pets the same day they check themselves. She also is considering developing stickers for calendars much like the monthly reminders that accompany flea and tick preventatives.

“Since dogs can’t do self exams, we will have to do them for them,” she said. 

Saba predicts that owners might have a hard time differentiating normal "fatty" mammary tissue from true masses. "Masses are usually firm," Saba said. "If there's ever any doubt, the owner should have the pet evaluated by the veterinarian."

Greer eventually wants to create an educational video that features a breast cancer survivor alongside a dog that beat mammary gland cancer.