Histiocytoma – everyone’s favorite tumor for dogs

I know, the words “favorite” and “tumor” in the same sentence is a little weird. Hear me out…

Imagine a lump showing up on your dog’s leg. It’s big. It’s nasty looking. Sometimes they bleed. You’re freaked, so you take your dog to your veterinarian to see what it is. You’re envisioning surgery for removal of the growth, or worse, this thing spreading and shortening your dog’s life. Will he need chemo? Is this going to keep growing? Will he get more? Will we have to amputate the leg? Sometimes our imagination gets a little carried away, and if you start reading crazy things on the web – forget about it!

Would you ever expect a tumor to go away on its own? Is that even possible???

This is not a joke! That gross looking tumor will seriously be gone in 3 months. This is one problem that you can literally ignore and it will go away. This is why the histiocytoma (pronounced HIS-tee-oh-si-TO-ma) is everyone’s favorite tumor! Here’s the scoop:

The tumors are made of cells that live in the skin, but function as part of the immune system, called histiocytes. (They may also be called Langerhans cells if you want to have a fun fact for a party.) A group of these goes a little crazy, no one knows why, and forms a mass. It can be small like a pea, or 2+ inches in diameter. They typically show up on the legs and feet, but I’ve seen them on the trunk as well. These tumors are typically found on young dogs, under the age of two. However, my 8-year-old dog decided to get one, so anything is possible!

They can be pink and peaceful looking, or bleeding and “angry looking”. Therefore, your veterinarian cannot diagnose it just by looking. Sure, the age of the dog and location may make her think histiocytoma right away, but we need to confirm.bernese mountain dog

How does a veterinarian make sure it is in fact a histiocytoma? Easy! We take a syringe with a needle, like we use to give a vaccine, and stick it in the mass. We pull out some cells and look at them under the microscope. The good news is histiocytomas are pretty loose about giving up cells, unlike other tumors who do not give up any. So we’ll easily be able to tell in about 10 minutes if this mass is a histiocytoma. In rare cases, the veterinarian may get a lot of blood contamination, making it hard to see the histiocytoma cells. If your vet wants to send the microscope slide to a pathology specialist and have them look at it to make sure, that’s never a bad idea.

Once your veterinarian confirms microscopically the tumor on your dog is in fact a histiocytoma, we always love to share good news. Go home, ignore it, and it will go away in 2-3 months! Can’t be more benign than that!

Admit it….you now have a favorite tumor too!

Posted in General health.


  1. My dog has this problem, we have operated 2 lumps, one on leg and the other one was in ear, but again one lump is growing from the ear at the same place. Please advice what should we do, is this the same histiocytoma or something else. Kindly suggest vaccine also if it is histiocytoma.
    It will be highly appreciated to receive your valuable answer. Thanks.

  2. I went to my vet this week when I noticed my dachshund had a small lump on the bottom of her ear. It had grown s bit in the last 2 weeks.
    The young vet I had never met before first said it looked like a cancer .
    She could give us a price to remove it costing $1200 to $1600. I was crying and my husband said can we byopcy it. She said if it starts bleeding they probly would have to operate and to get all the margins cut hLf her ear off. I freaked.
    My husband said please stick it and let’s check first
    She did and came back said she feels it’s a 90% chance it’s a Histiocytoma .
    Come back in 6 weeks it will most likely get bigger then fall off. To put a cream they gave me for her raw spot on her arm she scratches at all the time and has for years. She hunts for lizards all the time and I thought she had been bit by a spider. They said no
    I read some comments on your site from people and other sites and it says to never put a steroid cream on it. I don’t know if it’s a steroid cream but it’s by prescription. What should I put on it is one of the questions
    The other is I noticed on your site it mentioned it would be a good idea when they took a sample to send it out to a I think it’s called a pathologist to make sure that’s what it is
    She has always had allergies where she scratches the one place under the from armpit area also bites at her nails constantly
    We don’t have a lot of money and all these vets charge a fortune for everything
    She even added tooth cleaning cause she saw a small spot in the back tooth area
    We just had a physical 2 months ago and the vet said her teeth were fine.
    She’s 6 years old almost 7 in aug this year 3018 . What should we do?
    The estimate is $1660 with the 400.00 to clean her teeth
    They said since she’s under already it’s cjeaper to do it then
    I don’t have insurance my husband is having aeorta valve replacement surgery on the 31st and I just got out of the hospital from an appendectomy
    I feel our family is falling apart.
    She said she’s only 90% sure it’s a cutaneous histiocytoma
    What are your thoughts ?
    Thank you for your time.

    • Hey alexis, im a vet too.

      Corticoid drogs arent advised since they supress the immune system which in this case is not good since for this type of tumour to regress, you need your imune T cells working well!!

      If it’s a histiocytoma, you dont need to worry about it, for real!

  3. Alexis, I’m reading this now for the first time.If you don’t mind, can you follow up? Was it a histiocytoma after all? Thanks

  4. Hey alexis, im a vet too.

    Corticoid drogs arent advised since they supress the immune system which in this case is not good since for this type of tumour to regress, you need your imune T cells working well!!

    If it’s a histiocytoma, you dont need to worry about it, for real!

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