what can learning about breast cancer in dogs teach us about humans?
6 minute read
mammary tumours are more likely to occur in smaller breeds such as poodles, chihuahuas, dachshunds, and yorkie terriers. getty
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when rob and julia first noticed a small lump under the skin of their 12-year-old dog serena’s chest, they didn’t think too much of it. when they found another, they still weren’t concerned. when yet another lump formed, and all the lumps started to grow, the suburban vancouver couple became anxious.
“we took serena to the vet who said that, because they were soft and move around, they were probably just fatty tissue,” says julia. “we could have had them biopsied to rule out anything serious, but because the vet didn’t seem to think they were anything to worry about, we didn’t.”
dr. melissa meachem, dvm, assistant professor, department of veterinary pathology at the western college of veterinary medicine at the university of saskatchewan, confirms that these soft lumps are fairly common, especially in older dogs, and are usually benign.
according to the american kennel club, round lumps beneath the skin are called lipomas, made up entirely of fat cells, and almost always non-cancerous.
to rule out disease, says meachem, “your veterinarian would remove a small number of cells from those fatty masses using a fine needle aspirate for examination by a pathologist. that can tell us if those masses or bumps are coming from the mammary gland or are just fatty accumulation.”
she says the procedure, however, is invasive, costly, and involves anesthesia. and, if the mass proves to be cancerous, by then it’s often too late. her new research aims to change that.
new funding for better diagnostic tools
this summer, the denver, colorado-based morris animal foundation announced funding for a new study at the university of saskatchewan to develop improved diagnostic tools for detecting mammary cancer early in dogs, with meachem as lead researcher.
“the concern with our current process is that, usually by the time we [confirm cancer], about half of all mammary tumours are already malignant, and about half of those have already spread,” says meachem. “those patients have a very poor prognosis.
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“my research is looking at molecules that may act as biomarkers for early diagnosis,” she continues. “these molecules help tumours evade the animal’s immune system [so they can] hide out and grow unchecked and become more aggressive and malignant. it’s been shown that in human breast cancer, some tumours use these molecules as well. so i suspect that they also play a role in allowing mammary tumours in dogs to grow and become malignant. if we can catch them when they’re in these very early stages, we can remove the cancer and the dog can go on to live a very long life.”
breast cancer in dogs
while serena’s lumps turned out to be harmless, canine breast cancer, referred to as mammary tumour, is a real concern, primarily in intact, or un-spayed, dogs. meachem says it’s the most common tumour vets see in female dogs.
“we don’t know the exact prevalence in canada,” she says. “it’s such a complex issue because it is tied into whether the dog is intact or not, and the age at which they’re spayed. the research has shown that if you spay a dog before they go into heat, they have less than one per cent chance of developing a mammary tumour. that risk goes up exponentially after that. if you spay them after the first heat, they have an eight per cent risk. after the second heat they have a 26 per cent risk. and if you don’t spay them at all, their lifetime risk is between 25 and 35 per cent. it’s three to four times the risk of what we see in people.”
fortunately, canadians commonly spay and neuter their pets. however, meachem notes, there is currently a lot of discussion among experts about how early is too early, that spaying and neutering too soon could negatively affect joint and bone health. some experts recommend delaying spaying until two or three years of age (the spca suggests it be done between eight and 16 weeks). but, says meachem, “[delaying] could lead to an increased incidence of mammary tumours,” and that more research is needed.
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which breeds are most susceptible?
meachem says mammary tumours are more likely to occur in smaller breeds such as poodles, chihuahuas, dachshunds, and yorkie terriers. some larger breeds, however, are also at increased risk, such as those in the spaniel family — english springer and brittany spaniels — as well as boxers and german shepherds.
she says research has shown obesity can play a role in dogs developing mammary cancer, especially in the first year or two of life. “so keeping your dog in good body condition, not over-feeding them, and keeping them active can help.”
she says mammary tumours typically appear in middle age, around seven or eight years of age, peaking at 11 to 13, depending on the breed. also, dogs that naturally have a shorter life span tend to develop their tumours at a younger age.
male dogs can also develop mammary tumours but it’s very rare, primarily because these tumours are linked to the female hormones.
meachem says cats can also get mammary tumours but not as frequently as dogs. when they do occur in cats, though, the outcome is usually much worse — about 85 to 95 per cent of mammary tumours in cats are malignant.
treatment and prognosis
meachem says dogs who test positive for mammary cancer first have the tumours surgically removed. because up to 70 per cent of cases involve more than one tumour, they all need to be removed and assessed.
“that’s the first line for very benign, early lesions, and often the only thing that needs to happen. however, in cases where the tumour is malignant or invasive or there’s concern that it’s spread, typically these animals are also treated with chemotherapy and potentially non-steroidal anti-inflammatory drugs, depending on the stage.”
she says survival rates for benign early lesions are two years or more, especially if caught early and removed. these dogs continue to be at increased risk, however, for developing new tumours. if they’re closely monitored, that risk can be mitigated. dogs with high-grade disease, or cancer that’s spread, have a survival rate of weeks to a few months.
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meachem says just as women do self-breast exams, so too should pet owners examine their dogs and report any lumps or masses to their veterinarian. she says that two of the molecules she’s studying have been well-researched in human breast cancer. “there are similarities between breast cancer in women and mammary cancer in dogs, so there’s a lot we can learn for diagnostics and therapeutics in both. mammary cancer in animals can be a good model for breast cancer in people because our pets are exposed to the same lifestyle and environmental factors that we are.
“we just started our work this fall, so we’re very much at the beginnings of our project, but i’m really excited about it. hopefully this research can not only benefit dogs, but potentially impact breast cancer research in women as well.”
robin roberts is a vancouver-based writer.
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