Mast Cell Tumor vs. Histiocytoma: What's the Difference?
Learn how to tell apart two of the most common skin lumps in dogs.
Finding a lump on your dog is alarming. Two of the most common culprits are histiocytomas and mast cell tumors, and while they can look nearly identical, they’re very different conditions. Here’s what sets them apart, and why any new lump deserves a vet visit.
TL;DR
- Histiocytomas are benign, fast-growing, and common in young dogs; they often resolve on their own in 1–3 months.
- Mast cell tumors (MCTs) are the most common skin cancer in dogs, ranging from low to high grade (benign to aggressive).
- New lumps should always be checked by a vet. Fine needle aspiration is key to identifying the type of tumor.
- Histiocytoma treatment might include watchful waiting, while MCTs often require surgical removal and, sometimes, additional therapies.
- Diagnosing and treating canine skin tumors can get expensive, so pet insurance can help cover costs.
What are histiocytomas and mast cell tumors?
Histiocytomas and mast cell tumors both start as skin lumps, but they’re very different in nature.
A histiocytoma is a benign tumor caused by an overgrowth of Langerhans cells-these are immune cells found in the skin. They’re common in dogs under three years old and often resolve on their own in one to three months.
Mast cell tumors (MCTs), on the other hand, are the most common malignant skin tumors in dogs. They originate from mast cells, which are part of the immune system and play a role in allergic reactions. MCTs can come in various grades, from low-grade (less aggressive) to high-grade (fast-spreading and more dangerous).
Symptoms: What to look out for
At first glance, a mast cell tumor and a histiocytoma can look alarmingly similar. Both appear as raised bumps on your dog’s skin. Here’s how they compare:
- Histiocytoma: Usually small, button-shaped, and fast-growing. They’re typically hairless, smooth, and may appear red or inflamed. Histiocytomas are almost always benign.
- Mast cell tumor (MCT): These can vary in size and shape. They might appear as firm or soft lumps and don’t go away on their own. MCTs tend to ulcerate or bleed, and surrounding tissue may swell if the tumor releases histamine. Additionally, allergic reaction symptoms like things like vomiting, diarrhea, excessive swelling, or hives can also occur. Always consult a vet if you notice any of these signs.
Causes and risk factors
The causes of histiocytoma and mast cell tumors differ.
- Histiocytoma: These tumors are usually linked to overactive Langerhans cells and are more common in young dogs under three years old. Certain breeds like Boxers, Boston Terriers, and Scotties seem predisposed.
- Mast cell tumor: While the exact cause is unknown, certain breeds such as Boxers, Pugs, and Labrador Retrievers are more prone to developing MCTs. Genetics and environmental factors may also be part of the equation.
How do vets diagnose these lumps?
A vet’s expertise is critical to identify the nature of your dog’s lump. Diagnosis typically starts with a fine needle aspirate (FNA), a quick procedure where the vet collects cells from the lump using a syringe. Those cells are examined under a microscope to determine the type of tumor.
If the lump is an MCT, the vet may recommend a biopsy to grade the tumor. Grading indicates how aggressive the tumor is and helps shape the treatment plan. Histiocytomas rarely need further testing unless they don’t shrink over time.
Treatment options
Treatment depends on the diagnosis, the tumor type, and grade:
- Histiocytoma: Most of the time, these don’t need treatment as they resolve on their own within a few months. In rare cases where they persist, grow very large, or cause discomfort, surgical removal might be recommended.
- Mast cell tumor (MCT): Surgery is the primary treatment, with removal requiring wide margins to ensure all malignant cells are extracted. High-grade MCTs may require additional therapies like chemotherapy or targeted drugs (e.g., Palladia). The sooner these are removed, the better the prognosis.
Is pet insurance a helpful option?
Yes, and it’s worth thinking about before you’re sitting in a vet’s office with a diagnosis in hand.
Diagnosing and treating tumors can be costly. FNAs, biopsies, surgeries, follow-up therapies: it adds up faster than you’d expect. Lemonade’s base accident and illness policy can help cover diagnostics, treatments, and medications for illnesses like cancer, as long as the condition isn’t pre-existing. That means any signs or symptoms started after your policy was active and your waiting periods passed.
From there, you can build out your plan. The Visit Fee add-on can help cover exam fees for eligible conditions, and the Physical Therapy add-on can help with rehabilitation costs after major procedures like surgery.
The best time to look into coverage is before anything comes up.
Before we go
Finding a lump on your dog isn’t something to panic over, but it’s not something to ignore either. Whether it’s a benign histiocytoma or a mast cell tumor, catching and diagnosing it early makes a world of difference. Your vet is the best resource for determining next steps, don’t hesitate to make that appointment.
Frequently Asked Questions
Are histiocytomas in dogs painful?
Histiocytomas are generally not painful but may irritate your dog if they’re scratched or inflamed.
How can you tell if a lump is benign or malignant?
A fine needle aspirate or biopsy performed by your vet is the only way to determine if a lump is benign or malignant.
What happens if a mast cell tumor is left untreated?
Untreated mast cell tumors can grow, spread, and lead to more severe health problems, especially if they’re high-grade.
Do young dogs get mast cell tumors?
Mast cell tumors are more common in older dogs, but they can occasionally appear in younger ones, especially in high-risk breeds.
Does pet insurance cover cancer treatments?
Many pet insurance plans, including Lemonade, cover cancer treatments, as long as the condition isn’t pre-existing at the time of enrollment.
A few quick words, because we <3 our lawyers: This post is general in nature, and any statement in it doesn’t alter the terms, conditions, exclusions, or limitations of the policies issued, which differ according to your state of residence. You’re encouraged to discuss your specific circumstances with your own professional advisors. The purpose of this post is merely to provide you with info and insights you can use to make such discussions more productive! Naturally, all comments by, or references to, third parties represent their own views, and Lemonade assumes no responsibility for them. Coverage may not be available in all states. Please note that statements about coverages, policy management, claims processes, Giveback, and customer support apply to policies underwritten by Lemonade Insurance Company or Metromile Insurance Company, a Lemonade company, sold by Lemonade Insurance Agency, LLC. The statements do not apply to policies underwritten by other carriers.
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