How Can I Tell Whether a Lump on my Dog is Dangerous?

My eight-year-old black Lab has a small lump about the size of a golf ball on his chest. It's not under his arm but closer...

dogedit  |  Dec 2nd 2009

My eight-year-old black Lab has a small lump about the size of a golf ball on his chest. It’s not under his arm but closer to his underarm than his stomach. It’s hard and it moves. doesn’t feel connected to anything.

He seems fine. Eating, drinking, running, and in good health. He weighs about 65lbs. I just found it last night and am of course concerned. Any insight or ideas? Thank you in advance.

Brooklyn, NY

There is no way to tell with 100% certainty whether a lump is dangerous simply by looking at it (or by reading a description of it on the internet). However, several features of the mass you describe make me optimistic that it is not dangerous.

Owners generally have one overriding fear when they find a lump on their pet: is it cancer?

Malignant (cancerous) masses usually have poorly defined margins (it is hard to tell where the mass ends and normal tissue begins). They often grow into the tissue beneath them. They usually are irregular, and they may have tendrils extending from the center.

Benign (non-cancerous) masses usually have obvious margins. They often are spherical. They usually are freely mobile and they rarely grow into the underlying tissue.

Diane, based upon your description I suspect the mass on your dog is not cancer. It may be a type of fatty growth called a lipoma. Or it could be a cyst.

However, I must state emphatically that the mass needs to be sampled in oder to determine its nature. The simplest sampling method is called fine needle aspiration. This test is similar to a biopsy, but it is less painful and easier to perform. It yields a diagnosis in most cases.

I recommend that you visit your vet to have the mass assessed and tested. Hopefully the results will give you peace of mind.