Home Lumps and Skin Tumors on Dogs Histiocytomas

Histiocytomas in Dogs

By the Dog Health Handbook team · Updated · Fact-checked against current veterinary references (see sources)

Key takeaways

  • Benign red, button-like lumps, mostly in dogs under about 3 years old.
  • Most go away on their own within about 2 to 3 months.
  • Have it sampled: a histiocytoma can look like a mast cell tumor.
  • Removal if it hasn't shrunk in 1 to 2 months, or keeps bleeding or getting infected.
  • Not the same as histiocytic sarcoma, a separate, serious cancer.

Table of Contents

Research What it looks like Diagnosis Treatment Histiocytic sarcoma FAQ Sources

Skin and Coat Quicklinks

Overview Infections Irritation Parasites Yeast Infection Ringworm Lumps and Bumps Lipomas Cysts Histiocytomas Warts and Skin Tags Skin Cancer

A histiocytoma is a small, benign skin growth that mostly affects young dogs. It typically appears as a single raised, round, pink or red bump, often hairless, on the head, ear flaps or legs, and it can grow fast over the first few weeks.1,2,3 The good news is that most histiocytomas go away on their own within about 2 to 3 months, because the dog's immune system clears them.1,2,4 Because a histiocytoma can look like a mast cell tumor, have any new lump checked by your vet with a quick needle sample.3

See your vet if:

  • You find any new red, round lump, so it can be sampled and confirmed.3,2
  • A diagnosed histiocytoma hasn't started shrinking within 1 to 2 months.2
  • It's bleeding, badly ulcerated or infected, or your dog won't leave it alone.2,3
  • Several lumps appear, or the lump is on an older dog. These are less typical and need a closer look.2,4

What the Research Says

  • The most common lump in puppies. In a study of 2,554 skin lumps in dogs under 1 year old, 87% were histiocytomas. Only about 1 in 70 was a mast cell tumor.5
  • Young dogs. Most affected dogs are under about 3 years old, though histiocytomas can occur at any age.1,2
  • They usually regress. Spontaneous regression is the most common outcome, thought to be driven by immune cells that invade the growth.4
  • Multiple lumps are rare, seen in under 1 in 100 cases, and regrowth after removal is extremely rare.4

What a Histiocytoma Looks Like

  • A single, smooth, raised, button-like bump2,1
  • Pink or red, and often hairless1,3
  • Usually under 2 cm (about 3/4 inch) across, though it can reach 4 cm4,3
  • Most often on the head, face, ear flaps or legs1,3
  • Grows quickly over the first 1 to 4 weeks, and may become ulcerated (an open, raw surface), especially if licked2,3

Boxers are named as a higher-risk breed by all three main references used here. Others mentioned include Boston Terriers, English Bulldogs, Scottish Terriers, Greyhounds, Great Danes, Dachshunds and Labradors.1,2,3

How Vets Diagnose a Histiocytoma

A histiocytoma can't be told apart from a mast cell tumor just by looking at it.3 Your vet will usually take a fine-needle aspirate, which often gives an answer the same day. If the result is unclear, a small biopsy or removing the whole lump gives a definite diagnosis.2,1

Treatment: Wait and Watch, or Remove?

Once the diagnosis is confirmed, most vets recommend waiting, because most histiocytomas shrink and disappear within about 2 to 3 months.1,6 While you wait:

  • Stop your dog licking or scratching it. A cone or a soft sleeve may help.2
  • If it's ulcerated, keep it clean as your vet advises.2
  • Take a dated photo every week or two so you can see it shrinking.

Surgery is advised if the lump hasn't shrunk within 1 to 2 months, if ulceration, bleeding or infection can't be controlled, or if it's bothering your dog. Removal is usually a permanent cure.2,3 As a rough guide, PetMD puts surgery at about $300 to $500 in the US, with a lab biopsy adding about $200 to $400. Costs vary by area and clinic.3

Histiocytoma vs. Histiocytic Sarcoma

The names sound alike, but these are very different diseases. Histiocytic sarcoma is a serious cancer that comes from a different cell type. It mainly affects middle-aged and older dogs, especially Bernese Mountain Dogs, Flat-Coated Retrievers, Rottweilers and Golden Retrievers. It can start in the skin, joints, spleen, lungs or other organs, and it needs prompt treatment.7,8,9 A typical histiocytoma in a young dog is not a form of this cancer.8

See also lumps and bumps on dogs and mast cell tumors.

Frequently Asked Questions

Are histiocytomas cancerous?

No. They're benign growths that usually go away by themselves.

How long does a histiocytoma take to go away?

Usually about 2 to 3 months. Ask your vet about removal if it hasn't started shrinking within 1 to 2 months.

Can older dogs get histiocytomas?

Yes, but it's less common. A new lump in an older dog should always be sampled.

Is a histiocytoma contagious?

No.

Will it come back after removal?

Very rarely.

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Sources and further reading

This article was written and fact-checked on October 20, 2026 against current veterinary references and specialist guidelines:

  1. Villalobos AE. Lymphocytic, Histiocytic, and Related Cutaneous Tumors in Animals. Merck Veterinary Manual, Professional Version, reviewed August 2021, updated June 2026.
  2. Williams K, Weir M, Rest J. Cutaneous Histiocytoma in Dogs. VCA Canada Animal Hospitals, updated September 6, 2023.
  3. Kleszynski B. Histiocytoma in Dogs: Symptoms and Treatment. PetMD, September 9, 2026.
  4. Moore PF, UC Davis School of Veterinary Medicine. Histiocytoma Complex. UC Davis School of Veterinary Medicine, accessed October 2026.
  5. Kim D, Dobromylskyj MJ, O'Neill D, Smith KC. Skin masses in dogs under 1 year of age: 2554 cases (2006-2013). Journal of Small Animal Practice 63(1), 2022 (BSAVA summary, January 27, 2022).
  6. Villalobos AE. Tumors of the Skin in Dogs. Merck Veterinary Manual, Pet Owner Version, reviewed June 2018, updated April 2026.
  7. Moore PF, UC Davis School of Veterinary Medicine. Histiocytic sarcoma complex - general considerations. UC Davis School of Veterinary Medicine, accessed October 2026.
  8. Moore PF, UC Davis School of Veterinary Medicine. Histiocytosis. UC Davis School of Veterinary Medicine, revised 2016.
  9. Clinical Oncology Service, Ryan Veterinary Hospital of the University of Pennsylvania. Histiocytic Sarcoma in Dogs. Penn Vet client handout, accessed October 2026.

About this article

Last updated : new page, written using the Merck Veterinary Manual, VCA, PetMD, the UC Davis histiocytosis service, the University of Pennsylvania and a study of 2,554 skin lumps in young dogs.

This page is for general information and is not a substitute for an exam by your veterinarian.