Leo's Pet Care, 10598 N College Ave #200, Indianapolis, IN 46280

Veterinary Clinic and Animal Hospital serving Indianapolis and Carmel

Office Hours: Mon-Fri 8am-6pm, Sat 9am-12pm

Phone: (317) 721-7387 | Fax: 317-564-4902


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When to take a cat or dog with a lump to the vet.


This mast cell tumor would be very difficult to remove with 2cm margins.

“Doc, my dog’s got a lump, should I be worried about it?”

I get asked this question ALL. THE. TIME.

The answer is yes, no, and maybe. Let’s discuss.

“Never try to diagnose your pet’s lump with information you found on Google”

Please make this the last webpage you visit before taking your pet to the vet. Do not try to diagnose your pet’s lump over the internet. You’ll end up either freaking yourself out over something that may be nothing, or worse yet, ignoring something bad that could have been easily treated early.

That said, let’s move on…

First, some definitions. A tumor is an abnormal growth. Tumors can arise from any cell – skin tumor comes from skin, liver tumor comes from liver, mast cell tumor comes from inflammatory mast cells, etc. A tumor is not necessarily a bad thing, it’s just an abnormal thing. There are wide variations in how nervous I get about a tumor, depending on where it is, how long it’s been there, and importantly, how well behaved it is.

( Please visit the post I wrote once on Canine Histiocytoma – my favorite dog tumor, because it goes away on its own – to learn more about tumor vs. cancer vs. benign vs. malignant )

One of the reasons veterinarians hate tumors so much, is because there is such wide behavior in tumor behavior. To illustrate, let’s run through a list of four very common tumors:

1. HISTIOCYTOMA – A benign tumor of histiocytes, which are inflammatory cells. Usually look big and red and ulcerated and ugly, but often dry up and disappear within 3-4 months. Histiocytoma looks ugly, behaves nicely. My favorite tumor.

2. LIPOMA – A benign tumor of fat cells. Usually grow slowly under the skin, are freely movable, NOT attached to deeper tissues, have well defined borders, do NOT hurt the patient, can occur in multiples, and can usually be ignored. Lipomas don’t generally make dogs sick, they just sit there like… well, like lumps of fat, looking lumpy. Sometimes you can’t even see them, they’re so small. Lipomas look friendly, and behave nicely. My second favorite tumor, because they’re mostly harmless.

3. MAST CELL TUMOR – A potentially malignant tumor of inflammatory mast cells. Boxers like to grow these red lumps in their skin (I’m going to pick on Boxers because they grow mast cell tumors like it’s their job, but obviously other dogs get mast cell tumor as well). Mast cell tumors tend to send tiny little microscopic fingers growing out in all directions, making it very difficult to tell visually how big the tumor really is – like tree roots underground. Veterinary surgeons do our best to try to “get the whole thing” during the first surgery, often by cutting off an extra 2cm margin of normal looking skin around the lump. Taking that margin of normal skin always leaves a very large hole that is often difficult for the veterinarian to close. Worse, making such a big hole makes recovery similarly difficult because of skin tension, dog kicking at the incision with back feet, etc. And there’s no guarantee you’ve got the whole thing until the lab says “clean margins”, so there’s somewhat of an anxiety-inducing wait on lab results involved after surgery. Mast cell tumors like to recur in the same location, spread to other locations… Mast cell tumors look ugly, and behave badly.

4. MAMMARY TUMOR – A potentially malignant tumor. If you’re a cat with breast cancer, your chances are not good. If you’re a dog with breast cancer, your chances are slightly better, but your vet may need to remove more than one of your dog’s mammary glands. Sometimes we have to remove all eight to ten (ish) glands, which is a giant, expensive, painful surgery. Often so difficult and painful we split it into two separate surgeries. Every once in a while we can get away with taking just the lump, if we catch breast cancer in dogs soon enough. Mammary tumors in cats look ugly and behave badly. Mammary tumors in dogs look friendly at first, but usually end up behaving badly.

How do veterinarians evaluate tumors before surgically removing them?

What a fine question!

Veterinarians like to poke holes in things. It’s kind of our favorite. Basically any time a veterinarian sees something lumpy, we want to stick a needle into it, suck out some cells, squirt them onto a slide and send it in to the lab so they can try to identify it.

Cytology isn’t perfect. Cytology results can come back as one of the following:

1. BLOOD CONTAMINATION: There’s so much blood on this slide, we can’t tell what the tumor is. Cut the whole thing off and send it in please.
2. ACELLULAR: There are so few cells on this slide, we can’t tell what the tumor is. Cut the whole thing off and send it in please.
3. AMBIGUOUS: We see some cells we think are abnormal, but some that are normal, so we can’t tell what the tumor is. Cut the whole thing off and send it in please.
4. PRETTY DARN SURE: We’re pretty darn sure this is an XYZ (histiocytoma, lipoma, mammary tumor, etc, etc, etc). Cut the whole thing off and we’ll tell you for sure.
5. DEFINITIVE: This tumor is an XYZ, and here’s how we think you should handle it. (probably involving cutting the whole thing off and sending it in please, with or without giant margins)

Cytology, then, is a tool veterinarians use to decide if a tumor can be ignored and will go away, ignored but won’t go away, cut off with narrow margins, or cut off with wide margins.

Dr. Magnusson, you didn’t answer the question. When should I take a cat or dog with a lump to the vet?

Well, that’s easy. Every lump should be evaluated by a vet.

And ideally, every tumor should have cytology performed by that vet.

Sometimes we’ll then recommend surgery, sometimes we won’t. But you gotta go through steps 1 and 2 before you get to conclusion 3.

OK, but when should I really be worried?

Worry more if your pet’s lump….
1. Grows rapidly
2. Starts to bother your pet
3. Ulcerates or bleeds
4. Splits in half or spreads

If your pet has a lump, and you live in Indianapolis or Carmel or surrounding areas of Indiana, please call Leo’s Pet Care at 317-721-7387 to schedule your initial consultation and cytology, and we’ll give you a quote for tumor removal surgery at the same time!

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  • Dottie

    gosh how did you know i was wondering about arias tumor, i cant get to ur clinic asi live in muncie, i am glad i learned more on ur blog tho and the vet checked her lump in spet and said it wasnt life threatening but it was little then now its quarter size about the skin and abig fist knot under the skin.I worry cuz its near her spine, i am poor as dirt too so im afraid for her life and movements. also my chi mix wont leave it alone…

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