Reviewed by Paula Simons, DVM
August 1, 2022
Histiocytoma in dogs are benign tumors, meaning they are 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. You’ll most likely find these unsightly skin tumors on the face and extremities, but they can occur in any location.
There are other closely related condition knowns as histiocytic disorders. Unfortunately, these can be cancerous. They include the following:
- malignant histiocytosis
- cutaneous histiocytosis
- systemic histiocytosis
- histiocytic sarcoma
- histiocytic lymphoma
Canine cutaneous histiocytoma is a benign tumor that develops within the epidermis. Malignant fibrous histiocytomas tend to grow quickly but also spread to other parts of the body.
Identifying Histiocytomas in Dogs
Histiocytomas usually appear as small, hairless lumps. It’s not common for dogs to have multiple masses on their skin. Sometimes, however, they can appear red and ulcerated. They’re not pretty to look at and the ugly mass is often frightening for the dog owner who discovers it.
Symptoms of Histiocytomas in Dogs
- Appear as a small, raised button-like growth.
- Can appear on the head, ears, or limbs
- Is usually a single lump although there can be more.
- Painless and hairless
- Lump moves freely when touched.
- Tend to grow quickly in the first 1 to 4 weeks.
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.
It’s not possible to make a definitive diagnosis of any new lump on a dog. That can only be done through a fine needle aspiration or biopsy. That said, there are a few things to consider when trying to identify a new lump or bump on your dog.
Benign histiocytomas have certain characteristics in their appearance, growth, and feel. The following are 7 clinical signs.
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.
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.
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.
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
- Scottish Terriers
6. Histiocytoma in Dogs Originate in the Langerhans Cells
The langerhans 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.These 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:
- yelp or growl when you’re close to the dog
- sensitivity to touch
- unusually quiet
- 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.
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 – Idiopathic
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 surgical removal.
However, if the tumor grows and doesn’t appear to be shrinking in the given time frame, surgery might be required. The veterinarian will assess the mass’s location, size, appearance and the degree of inflammation.
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.
Dogs who develop a cutaneous histiocytoma generally have an excellent prognosis. They are generally diagnosed through cytopathologic examination. The examination involves the examination of individual cells under a microscope. The veterinarian will gather cell samples via fluid or a small piece of tissue.
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.
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.
Frequently Asked Questions About Histiocytomas in Dogs
How do you treat histiocyoma in dogs?
Surgical intervention may be suggested if the lump is still in place after three months. In fact, if the lump is small enough, it may be possible for the vet to remove it through cryosurgery.
Cryosurgery uses extreme cold produced by liquid nitrogen or argon gas. When liquid nitrogen reached between -346 and -320 degrees Fahrenheit it instantly freezes the tumor. This is the same procedure used to freeze warts off of skin.
A local anesthetic can be used before the application. The procedure is usually effective at freezing the histiocytoma right off the skin.
Will a histiocytoma go away on its own?
These skin masses typically regress spontaneously with a couple of months. If they don’t regress on their own, there’s a risk of the mass becoming ulcerated. Secondary infection and bleeding are a possibility.
Unfortunately, secondary infections can lead to serious outcomes.
Could the histiocytoma fall off?
Histiocytomas do not actually fall off. Instead, they tend to shrink and get almost reabsorbed by the body.
Are histiocytomas cancerous?
Sometimes they can progress into cancer. This might occur in older dogs with inadequate immune systems.
Summing It UP
It’s important to realize that not all lumps in dogs are cancerous. Naturally, as dog parents, we panic a little when we see something new and unusual growing out of our dogs.
It’s wise to have any new lumps or bumps examined by a veterinarian. This will help reassure you and initiate early diagnosis in case it is something more serious.
It’s usually dogs under 2 years of age that develop histiocytomas and the lumps often go away on their own. No intervention is necessary most of the time. That said, if the veterinarian is concerned about the growth because it isn’t regressing (for example) surgical removal may be suggested.
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