What is a mast cell tumour in dogs, and how serious is it?
A mast cell tumour (MCT) is one of the most common skin cancers diagnosed in dogs. It arises from mast cells — immune cells found in connective tissue — and can range from a slow-growing, localised lump to an aggressive cancer that spreads to lymph nodes and internal organs. Prognosis depends heavily on tumour grade, location, and how early treatment begins.
MaxPetz in Delhi provides veterinary cancer care for dogs diagnosed with mast cell tumours, combining clinical assessment, histopathological grading, and tailored treatment planning to support the best possible outcome for your pet.
Key fact: MCTs account for a significant proportion of all canine skin tumours, making early detection and accurate grading essential to effective treatment.
What does a mast cell tumour look like on a dog?
Mast cell tumours are often called the "great imitators" in veterinary oncology because they can look like almost any skin lesion. There is no single appearance that reliably identifies an MCT without a biopsy or fine-needle aspirate.
- A raised, firm or soft lump on or just beneath the skin
- A hairless or ulcerated patch of skin
- A lump that changes size — swelling and shrinking over days (known as Darier's sign)
- Redness, itching, or inflammation around the mass
- A lesion that has been present for months with little change, or one that grows rapidly
Common locations include the trunk, limbs, and perineal region, though MCTs can appear anywhere on the body. Any new or changing skin lump should be assessed by a veterinarian promptly — do not wait to see if it resolves on its own.
Warning: Manipulating or repeatedly pressing a mast cell tumour can cause degranulation — the release of histamine and other chemicals — leading to local swelling, redness, and in rare cases systemic reactions. Avoid squeezing or irritating any undiagnosed skin lump.
How are mast cell tumours graded, and does grade affect prognosis?
Grading is the single most important factor in predicting how an MCT will behave. A veterinary pathologist examines a tissue sample under a microscope and assigns a grade based on cell appearance and behaviour. Two grading systems are in current use:
| Grade / Category | Behaviour | General Outlook |
|---|---|---|
| Patnaik Grade I | Well-differentiated, confined to skin | Favourable with complete surgical removal |
| Patnaik Grade II | Intermediate; variable behaviour | Depends on additional markers (Ki-67, c-Kit) |
| Patnaik Grade III | Poorly differentiated, aggressive | Higher risk of spread; multimodal treatment often needed |
| Kiupel Low Grade | Low mitotic activity | Generally favourable prognosis |
| Kiupel High Grade | High mitotic activity | More aggressive; shorter median survival without treatment |
A Grade 2 mast cell tumour is considered intermediate and can be serious depending on additional prognostic markers. Your veterinarian may recommend immunohistochemistry (Ki-67 proliferation index, c-Kit mutation testing) to better characterise Grade 2 tumours and guide treatment decisions.
Can mast cell tumours in dogs be cured with surgery?
Surgery is the primary treatment for most localised mast cell tumours and offers the best chance of long-term control when the tumour is completely excised with adequate margins. Whether surgery alone is curative depends on grade, location, and margin status.
- Wide surgical excision — The standard approach. The surgeon removes the tumour plus a margin of surrounding healthy tissue (typically 2–3 cm laterally and one fascial plane deep) to reduce the risk of local recurrence.
- Sentinel lymph node evaluation — Nearby lymph nodes are assessed to determine whether the cancer has spread regionally.
- Radiation therapy — Recommended when complete surgical margins cannot be achieved, or as adjuvant therapy for high-grade tumours.
- Medical management — Tyrosine kinase inhibitors (e.g. toceranib, masitinib) are used for inoperable, recurrent, or metastatic MCTs. Antihistamines and proton pump inhibitors are used to manage systemic effects of histamine release.
- Chemotherapy — May be used alongside surgery or targeted therapy for aggressive or disseminated disease.
For Grade I and completely excised Grade II tumours, surgery alone frequently results in long-term remission. High-grade or incompletely excised tumours typically require multimodal therapy.
Tip: Pre-operative staging — including fine-needle aspirate of regional lymph nodes, abdominal ultrasound, and buffy coat examination — helps determine whether the disease is localised before committing to surgery.
What is the prognosis for dogs with mast cell tumours, and do they spread?
Prognosis for canine MCT varies considerably. Key factors that influence outcome include tumour grade, completeness of surgical margins, lymph node involvement, presence of distant metastasis, and tumour location.
- Spread (metastasis): MCTs can spread to regional lymph nodes, spleen, liver, bone marrow, and other organs. High-grade tumours carry a significantly higher risk of metastasis than low-grade tumours.
- Growth rate: Low-grade MCTs may remain stable for months to years. High-grade tumours can enlarge rapidly — sometimes within days to weeks.
- Location: Tumours on the muzzle, nail bed, inguinal region, or mucocutaneous junctions tend to behave more aggressively regardless of histological grade.
- Multiple tumours: Dogs presenting with multiple simultaneous MCTs are not automatically considered to have metastatic disease; each tumour should be assessed individually.
Dogs with completely excised, low-grade MCTs frequently live normal lifespans. Dogs with high-grade or metastatic disease have a more guarded prognosis, though targeted therapies have extended survival times in many cases. Your veterinarian will discuss realistic expectations based on your dog's specific findings.
When should you bring your dog to a vet for a skin lump?
Do not adopt a wait-and-see approach with unexplained skin lumps in dogs. Seek veterinary assessment promptly if you notice any of the following:
- A new lump or bump that has been present for more than 2–4 weeks without resolving
- Any lump that is growing, changing shape, or changing colour
- A mass that appears ulcerated, weeping, or crusted
- A lump that causes your dog to scratch, lick, or bite at it persistently
- Swelling or redness around an existing lump that fluctuates in size
- Your dog showing systemic signs alongside a skin lump — vomiting, diarrhoea, lethargy, or reduced appetite — which may indicate histamine release from an MCT
- Any lump in a high-risk location: muzzle, groin, perianal area, or between the toes
Early diagnosis allows for staging before the tumour spreads, wider surgical margins, and a greater likelihood of complete excision — all of which improve long-term outcomes.
How does MaxPetz Delhi support dogs diagnosed with mast cell tumours?
MaxPetz in Delhi offers veterinary cancer care that covers the full diagnostic and treatment pathway for dogs with mast cell tumours — from initial fine-needle aspirate and histopathological grading through to surgical planning, post-operative monitoring, and long-term follow-up. The clinic combines cutting-edge veterinary technology with compassionate, individualised care for each patient.
The care team works with pet owners to explain grading results, staging findings, and treatment options in clear terms, so that decisions are made collaboratively and with a full understanding of what each pathway involves. For complex or high-grade cases, the team can discuss referral pathways and adjuvant therapy options appropriate to your dog's diagnosis.
To discuss your dog's skin lump or a recent MCT diagnosis with the MaxPetz Delhi team, use the Cancer Care booking form on this page or explore our mast cell tumour surgery information. You can also speak directly with a veterinary specialist by completing the consultation request form above.
Book a consultation at MaxPetz Delhi
Use the booking form on this page to arrange a cancer care assessment for your dog. Early evaluation gives your pet the best possible start to treatment.