Histiocytoma: The Lump in Young Dogs That Often Goes Away
Histiocytomas are benign skin tumours that often shrink on their own. A Portuguese study shows which dogs get them, at what age, and where on the body.
Written by thecanineledger
Any new lump should be checked by a vet. Don’t assume a lump is a histiocytoma because your dog is young.
Our note: This advice is ours, including our line that a histiocytoma can look like lumps that are not benign. Show your vet any new, fast-growing lump.
In a Portuguese study of 359 confirmed histiocytomas, 48.8% were in dogs aged 2 or under. The authors describe the tumour as “a benign Langerhans‐cell tumour that often regresses spontaneously via inflammation.” (De Moura et al., Veterinary Dermatology 2026). Langerhans cells are immune cells in the skin. Regresses means it shrinks and goes away.
While that sounds reassuring, a histiocytoma can look like other lumps, including ones that are not benign. A vet needs to confirm it.
→ Found a Lump? Why Your Vet Should Put a Needle in It · → Mast Cell Tumours: What the Grade Means
1. The study
The cases. The researchers analysed 359 histiocytomas confirmed by a pathologist at one private laboratory in Lisbon, from January 2020 to January 2022.
Rates. They used Portugal’s national dog register to estimate how often the tumour occurs. In the Lisbon–Setúbal area it was diagnosed in about 4 dogs per 10,000 each year.
Funding. A Lisbon university and a Portuguese university oncology project supported the work. The authors declare no conflicts of interest.
2. Which dogs get them
Age. Nearly half the cases were in dogs aged 2 or under. The authors found three age bands, roughly under 1.5 years, 1.5 to 3.5 years, and over 3.5 years.
Sex. 58.5% of cases were in males.
Breed. Compared with mixed-breed dogs, risk was highest in:
| Breed | Risk compared with mixed breeds |
|---|---|
| French Bulldog | 11.5 times |
| Boxer | 8.3 times |
The paper cites earlier studies that also found higher odds in Boxers and French Bulldogs, among others.
Our note: This is one Portuguese laboratory’s caseload. Breed risks may differ elsewhere.
3. Where they appear
The legs were the most common site, followed by the head. Some breeds showed patterns. Jack Russell Terriers mostly had tumours on the legs. Cocker Spaniels, Yorkshire Terriers and Beagles more often had them on the head or ears.
The average lump was 1.6 cm across.
4. What the study can’t tell you
Only lumps that were sent to a lab. The authors note their figures “may under‐ascertain CCH that regress without biopsy confirmation and may reflect referral patterns.” Lumps that shrank on their own without testing weren’t counted.
How long they take to go. The paper cites earlier work saying histiocytomas usually go within about 2 to 3 months. This study didn’t measure that.
Our note: Whether to watch or remove a confirmed histiocytoma is a decision for you and your vet.
5. If your dog has a new lump
- Have it checked, whatever your dog’s age.
- Ask whether a needle sample is needed to tell what it is.
- If it is a histiocytoma, ask how long to wait and what changes should bring you back.
Our note: These points are ours, not the study’s.
6. What we could not verify
| Commonly said | What we found |
|---|---|
| “Histiocytomas only happen in puppies” | No. About half were in dogs over 2. |
| “A red button lump in a young dog is always harmless” | Not safe to assume. Only testing confirms what a lump is. |
| “Histiocytomas always go away” | Often, the paper says. This study didn’t follow the lumps over time. |
Sources
- De Moura C, Pinello K, Catarino J, et al. Epidemiology of Canine Cutaneous Histiocytoma: Insights From Age and Topographic Clustering. Vet Dermatol 2026: 359 laboratory-confirmed cases, Lisbon, 2020 to 2022. University funding; no conflicts declared
Always confirm with your vet before acting on anything on this page.