One of the most common lumps that owners find on their dogs is the lipoma. When I tell owners the lump they were worried about is a lipoma, it’s met with relief, since these are not cancerous. But they are not always 100% benign.
A lipoma is defined as a mass of fat, AKA a “fatty tumor”, often encapsulated, giving it defined borders. It can be freely movable under the skin, or firmly attached to the muscle underneath. They are always under the skin, but can be directly underneath, or some can be embedded within the layers of subcutaneous tissue.
So while lipomas can present a variety of ways, they are still considered benign. Some breeds are more prone to developing them than others, and they increase with age. In my experience, chocolate labs seems to be the poster child of lipomas, but they can occur in any breed.
Often dogs who develop one lipoma will develop more. They can start out small, but some can grow exceptionally large. I’ve removed lipomas that were the size of volleyballs! So while they are not cancer, and technically benign, a volleyball sized mass that prevents a dog from lying down comfortably is hardly benign.
It’s important to monitor your dog’s lipomas, and if one starts getting bigger, it’s better to remove it sooner, when it’s small, than later! Also, I’ve had dogs with 15 lipomas, and then the new lump they get is NOT a lipoma! So while it’s true that dogs who develop one lipoma will develop more, it’s important to not drop our guard. I have a pit bull patient with 5 lipomas. I have performed fine needle aspirates on all of them. That means I poked each one with a needle, pulled out some cells, and looked at them on the microscope to determine the lumps were lipomas. She grew a new lump that seemed different. Sure enough, when I performed the aspirate, I did not see fat cells, but mast cells! Surprise- this was a different kind of mass, and a cancerous one! So while we don’t panic over new lumps and bumps on our old lumpy dogs, we want to monitor for new developments.
Lipomas can be removed surgically, and they are normally pretty easy. Since they are primarily fat, they tend to not have a large blood supply. The only problem is all the fat make my surgical instruments feel like I rubbed them in crisco!
While lipomas are common and benign, we want to remove them before they become obnoxious, and be aware of any new lumps on our older dogs. But still, hearing the lump on your dog is benign is always good news.