Mammary Cancer in Dogs

You probably know the statistics. About 1 in 8 U.S. women (about 12%) will develop invasive breast cancer over the course of her lifetime. In 2019, an estimated 268,600 new cases of invasive breast cancer are expected to be diagnosed in women in the U.S., along with 62,930 new cases of non-invasive (in situ) breast cancer.*

I wrote “you probably know these stats” because breast cancer is possibly the most widely publicized cancer in the country. There are widespread breast cancer awareness campaigns, and ongoing research. But did you know that the prevalence of mammary cancer in adult intact female dogs is even higher than that? 

Mammary Cancer is Common in Unspayed Females

Mammary cancer is very common in dogs, especially those that are not spayed or neutered. It’s more common in females than males, in fact one in four unspayed bitches is affected. Mammary tumors are a very widespread issue, but owners of female dogs just aren’t aware of the risk. Unfortunately I have seen quite a few cases lately.

Mammary Cancer is Avoidable

If female puppies are spayed before their first heat cycle, it almost eliminates their risk of mammary cancer completely. A study of the incidence of canine mammary tumors showed that tumors occurred in 0.05% of females spayed before the first heat cycle. This incidence increased to 8% or 26% when the animals were spayed after the first or second heat. If the animal was spayed after this period of time, the risk of developing mammary cancer was the same as for an unspayed bitch.**

There are, of course, people that want to breed their bitches or not spay until they are fully grown because they are a large, or giant breed dog. But these statistics show that this is a decision that needs to be discussed with your vet to decide the best course of action for your pet. To avoid the chance of your female contracting mammary cancer have her spayed preferably before her first, but definitely after her second heat cycle.

When & How to Check Your Dog for Mammary Tumors

Mammary cancer is most commonly diagnosed in adult female dogs aged 9 to 12 years old, followed by 5 to 8-year-old females. Pure breeds accounted for 80% of submissions in the study. The Poodle, Cocker Spaniel and German Shepherd breeds were consistently affected.**

Mammary cancer tumor locations

Graphic by MarVistaVet

But when should you begin to check your female dog for growths? Always keep an eye out for unusual lumps. Report anything unusual to your vet as soon as you find something. But start actively checking when your female is 6 years old. This includes both unspayed female dogs and female dogs that were spayed as adults.

Unfamiliar with the normal mammary anatomy of the female dog? Here’s a quick lesson. You will find five sets of mammary glands as shown, though the average female dog has only nine. Normal glands should be soft and pliant, especially towards the rear legs. There should be no firm lumps. If a lump is detected, see your veterinarian at once regarding possible removal. Most tumors occur in the glands nearest the rear legs.***

Schedule an Appointment Today

You can find more detailed and very useful information on mammary tumors in dogs using this link to the Veterinary Partner website. But if you have any concerns, or find any unusual lumps on your pet, call 480.774.6995 to schedule a mobile vet or clinic appointment with Compassionate Animal Care today.



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