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7 Clinical Signs of Histiocytoma in Dogs

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Histiocytoma in dogs are benign, meaning non-cancerous.  They usually occur in dogs under 2 years of age and affect certain breeds including Bull Terriers, Boston Terriers, and Boxers, to name a few. 

Unlike its cousin the mast cell tumor, histiocytomas are more of a nuisance than a danger.

Complete Guide to Benign Histiocytoma in Dogs

The following list provides the signs, symptoms, and typical characteristics of these benign tumors.  Also known as cutaneous histiocytoma in dogs, these tumors usually appear on the head, neck, ears, or limbs. 

1 Fast Growing

Histiocytoma in dogs are fast-growing tumors.  They have a slightly menacing look that tends to put dog owners in a state of panic.

Expect the tumor to be pink or reddish in color with a smooth top. Be prepared, because they are disgusting.  Most of the time there’s only one tumor; however, it is possible for there to be multiple masses.

Benign tumors are moveable when palpated.

2. Itchy

Initially, this tumor may bother you more than it does your dog. They’re not pretty to look at!  As wounds heal, the body releases histamine as an autoimmune response and that makes the tumor very itchy.

At this stage, it’s important to prevent your dog from scratching or biting it. 

Depending on the tumor’s location, you may need to use an Elizabethan collar or other type of barrier to prevent that. When your dog starts scratching the tumor, you know it’s starting to heal.

3. Will Cure Themselves

As much as you want to get that lump removed, it’s important to know that histiocytoma in dogs usually resolve on their own within 3 months.  

There’s never anything simple when it comes to dogs and medical procedures. If your dog is young and is presenting with this issue, the veterinarian will likely suspect histiocytoma. 

Depending on the veterinarian’s experience with these, he/she may suggest waiting until it shows signs of regression.  Other veterinarians may suggest aspirating some cells to view under a microscope.

This is just my opinion, but I would rather be safe than sorry. If it were my dog, I wouldn’t feel comfortable with a wait-and-see approach. 

No matter how much reassurance I had, the best reassurance comes from a laboratory test.  I would want to know whether it was benign (most likely scenario) or malignant.

4. Only in Young Dogs

This type of tumor typically presents in very young dogs, usually under two or three years of age.  However, it can occur in older dogs from time to time. 

Histiocytoma in dogs look and feel the same no matter the age of the dog.

Please note:  There’s a lot of variation in the age of onset, although younger than 3 years of age appears the most widely accepted range. 

Tumor or Growth on a Dog
Watch this video on YouTube.

5. Common Among Certain Breeds

 The following breeds are susceptible to histiocytoma in dogs:

  • Bull Terriers
  • Boston Terriers
  • American Staffordshire Terriers
  • Shar Pei
  • Labrador Retrievers
  • Boxers
  • Scottish Terriers
  • Greyhounds

6. Histiocytoma in Dogs Originate in the Langheran Cells

The Langheran cells are found in all layers of the skin, but are most prominent in the stratum spinosum (the third layer of the epidermis).

These cells form part of your dog’s immune response and work to prevent dangerous microbes from passing through. 

Bacterial and viral microorganisms are detained by these cells. In addition, the Langheran cells work to protect the body against skin damage caused by UVB radiation.

Histiocytoma in dogs occurs when the cells grow and divide too much. This action results in small, red, button shaped tumors.  Sometimes there is more than one tumor (mass), but it is unlikely.

7. Not Painful

Histiocytoma in dogs are not painful. However, depending on the tumor’s location, the tumor can be irritated by friction and that can cause the tumor to ulcerate.  A scratched or ulcerated tumor is susceptible to bacterial infection.

How can you tell the dog is not in pain?  The following signs of pain have NOT been reported in dogs with histiocytoma:

  • agitation
  • yelp or growl when you’re close to the dog
  • sensitivity to touch
  • unusually quiet
  • depressed
  • might stop eating
  • shallow breathing (possible)

Size & Appearance

Expect to see a small, perfectly round and raised lump.  Histiocytoma in dogs tend to grow very fast in the first four weeks until the settle at about 2.5 cm.

Button Shaped

This is pretty self-explanatory, but histiocytoma in dogs look like buttons and so are aptly named “button tumors”.

Red & Raised

These tumors are pink – red and are raised on the skin.  It’s tempting to want to mess with a growth on your dog’s skin as a way to try and get rid of it faster.

If you’re the kind of person who doesn’t like to wait, you’re out of luck. This tumor takes a few months to regress and during that time, it might feel like you’re going out of your mind trying to keep your dog from scratching.

Unknown Cause

The originating cause is not clear.


If the veterinarian is certain that it’s nothing more serious, he/she will likely suggest a wait-and-see approach. 

They know that the tumor will begin to regress within a few months.  By waiting, you don’t encounter unnecessary expense and your dog doesn’t have to risk complications from surgery.

However, if the tumor grows and doesn’t appear to be shrinking in the given time frame, surgery might be required.


To diagnosis histiocytoma in dogs, the veterinarian may want to do blood tests, urinalysis, and possibly aspirate the tumor to get a closer look under a microscope.  Practices vary from clinic to clinic.

Histiocytic Diseases are Divided Into Three Categories Including:

  • Nonmalignant Nonneoplastic (meaning there is no cancerous tumor)
  • Nonmalignant Neoplastic (non cancerous tumor)
  • Malignant Neoplastic (cancerous tumor)

Nonmalignant Nonneoplastic (Benign)

Within this category, you will find:

  • Reactive Cutaneous Histiocytosis
  • Reactive Systemic Histiocytosis

The cutaneous version of the disease can show up anywhere on the body and are not itchy.  There may be multiple nodules but they are not painful.

The systemic version of this reacts very similarly, but can also affect the organs other than the skin.

Nonmalignant Neoplastic (Benign)

  • Cutaneous Histiocytoma (benign – non cancerous)

This is the type of tumor this post is about and all of the information about it is in the paragraphs above.

Malignant Neoplastic (Cancer)

  • Localized Histiocytic Sarcoma (cancerous and spreading tumor)

Prognosis for this is very poor because by the time you see a tumor on the skin, the cancer has most likely already spread.

Malignant Histiocytosis

This is a rare hereditary disease found in Bernese Mountain dogs. In this disease, the liver, spleen, and central nervous system can be affected.  The disease moves quickly and is, ultimately, fatal. 

It is considered a disorder of the mononuclear phagocyte system.

 Mast Cell Tumors Versus Histiocytoma in Dogs

Mast cell tumors are concerning if they are not caught early.  They occur within the cells of the connective tissue and will eventually metastasize to other organs.  Histiocytomas also originate within cells but are not cancerous.

I want to thank you for reading this post and I hope you’ll be back soon. 


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