The grey area between benign and cancerous masses on dogs

Every day I have an owner show me a lump on their dog and express concern about what it is. Fortunately, the vast majority of these masses are cysts, skin tags, lipomas, or other non-threatening growths, much to the relief of the owner. Occasionally, a lump will be cancerous, and then of course we have a conversation.

I want to talk about the other category that they don’t teach in vet school, it’s not in text books, but it’s in the real world. It’s the grey area between benign and cancerous. I know, how on earth can there be a middle zone here!?! Well, there’s a couple ways.

The definition of benign is harmless. It’s a word pet owners love to hear when we are talking about masses on their pet! When I tell them a mass or growth is benign, there’s always a sigh of relief, and we move on…. or do we?

A mass can be benign in that it is not cancer, but it might not necessarily be harmless. For instance, I have many labs I see who develop large lipomas all over their bodies. These are fatty tumors (literally growths of fat) that are not cancer and are in fact technically benign. However, is it really harmless when the mass reaches the size of a volleyball and prevents the dog from turning his head one direction? Or the softball sized mass is in the crook of the elbow, preventing the dog from lying down comfortably? I have many owners who say “but it’s benign” when I recommend surgical removal, and we have to discuss how harmless it really is when it affects the dog’s daily comfort or mobility.

benign lump

Labrador retrievers are the poster child of lipomas (benign fatty tumors) although any breed and have them.

Other tumors that are benign can be more irritation to the owner than the dog! Some cysts will rupture and bleed, causing discomfort for the pet, but a mess for the owner. Some dogs will find a benign skin tag and lick it and lick it until it becomes infected. That’s taking a benign mass and turning it into a problem! These are often surgically removed to improve everyone’s quality of life.

So just because a lump, tumor, or mass is labelled benign doesn’t necessarily mean it’s completely harmless. The other side of this is tumors that are cancerous that are no big deal. Often, when I test a lump and it’s cancer, the owners are obviously very upset and want to know what action should be taken next. And in most cases, we do want to act promptly and smartly when we diagnose cancer…but not always.

I had a pug patient who loved to produce tumors called mast cell tumors. These come in many varieties, from wimpy to super aggressive, and we can’t tell which it is until we take off the tumor and send it to the lab for testing. Well, this kiddo had 3 tumors taken off, and they came back as the wimpy kind. Good news! But 2 months later more popped up. We dutifully took those off, still the wimpy kind. Two months later MORE tumors popped up. This was getting old, and the dog was going to be franken-dog if we kept slicing tumors off every part of him! Turns out, when they are these wimpy tumors and in these numbers, it’s OK to let them go. He’s doing great (a bit lumpy when you pet him) but putting him through more and more surgery wasn’t good for him, and the tumors, although technically “cancer,” are not harming him in any way.

Other tumors that are cancer that sometimes do not get me excited are spindle cells tumors. (I have a whole article about them here). Often (of course, not always) these are on the skin and look ugly, but they do not spread or affect the dog otherwise. So technically the dog is walking around with “cancer” and we’re OK with it.

My take home message is to keep an open mind. Benign is good news, but might not mean that mass gets ignored. And cancer isn’t always big bad and scary. These are labels, but there are some grey areas in between.

Posted in Dermatology.

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