Dr. Barchas,

I had my dog spayed around a month and half ago. She’s 5 to 7 years old (the vet thinks) and she had what they thought was a mammary tumor. About two to three weeks ago we found a small B.B.-sized bump, and two more tiny bumps, around the nipple near where the other tumor was removed. Should we go ahead and get the tumors removed? She’s a Yorkshire Terrier mix and I was told by a breeder of Yorkies that they just get these little tumors and that that it’s common. Is this true?

Thanks for all your help,

Jen

Carson City, NV

The short answer is yes, canine breast tumors are common. And yes, suspected breast tumors should be removed.

Common breast tumors in dogs (like all tumors) come in two varieties: benign and malignant. Benign breast tumors (called mammary adenomas) do not generally spread to distant sites in the body, although dogs often develop multiple benign tumors simultaneously or sequentially. Malignant tumors have a tendency to spread.

Jen, tumors like the ones you describe have basically even odds of being malignant. Malignant tumors often spread from one breast to another on the same side. They also can spread to the lymph nodes in the groin. Most dangerously, they can spread to the lungs and cause fatal complications.

Biopsy is the only reliable way to differentiate benign breast tumors from malignant ones. Simple aspiration of the masses (a quick procedure that usually can be done without anesthesia or sedation) rarely distinguishes between them. The simplest way to biopsy a mammary mass is to remove it. The veterinary experts I know universally recommend removing mammary masses.

But before you jump to surgery, there are a few things to consider. First, your dog has already had one mammary mass removed. Was it benign or malignant? Your vet should be able to provide you with that information. If the mass was malignant, then more aggressive intervention (such as removing all of the mammary glands on the affected side) may be recommended.

Second, I (and most experts I know) do not recommend surgical removal of mammary tumors without first performing chest X-rays to check for obvious spread of the disease into the lungs. Bluntly put: If the masses are cancerous and they have already spread, it might not be worth putting your girl through a surgery.

Hopefully your girl’s radiographs will be clear and the masses will be determined to be benign. If so, you will still need to monitor for the development of new ones, and seek treatment for any new masses that arise. If the masses are found to be malignant, then your vet may (or may not) determine that another, more radical surgery is necessary.

Readers in general should know that canine breast tumors are highly preventable with early spaying. Dogs spayed before their first heat are approximately 23 times less likely to develop breast tumors than dogs who are spayed after their third heat. Although the total individual health benefits of spaying are a subject of some contention among experts (for what it’s worth, I believe that the health benefits of early spaying outweigh the benefits of postponing spaying or not spaying at all), the effect of spaying on reducing breast tumor development is well-documented.

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