Mast Cell Tumors in Dogs - a Skin Tumor With Unpredictable Behavior
Mast Cell Tumors in Dogs - a Skin Tumor With Unpredictable Behavior
Important note: Fidello is not a veterinarian. This page is meant to inform you and does not provide a diagnosis. If you are worried about your dog's health, or recognize the signs described below, always contact a veterinarian.
A mast cell tumor, also called a mastocytoma, is the most common malignant or potentially malignant skin tumor in dogs. Its behavior varies widely: some mast cell tumors grow for years without much change and can be fully resolved with a single surgery, while others grow quickly and can spread. Because this difference cannot be judged by eye, it is important to have every new lump on your dog checked by a veterinarian.
What is a mast cell tumor?
Mast cells are immune cells that naturally occur in the skin and other tissues. They contain granules holding substances such as histamine, heparin and enzymes, and normally play a role in allergic reactions and defense against parasites. In a mast cell tumor, these cells divide in an uncontrolled way and form a lump, usually in the skin, though rarely also in internal organs such as the spleen or intestines. The exact cause is not known in every dog; in a subset of tumors, an acquired change in a specific cell-receptor gene (KIT) contributes to the uncontrolled division of the cells.
Which dogs are at risk?
Mast cell tumors can occur in any dog, but are reported more often in certain breeds, including the Boxer, French Bulldog, English Bulldog, Golden Retriever, Labrador Retriever, Shar-Pei, Dachshund and Bull Terrier, suggesting a hereditary component in some cases. The condition is more common in older dogs, though it can also occur in younger animals; Boxers, for example, relatively often develop the tumor at a somewhat younger age, generally with a more favorable course. In some breeds, such as the Shar-Pei, a more aggressive course is reported more often, while breeds such as the Pug more often develop multiple, mildly behaving tumors at once. This breed sensitivity is an indication based on reports in the veterinary literature, not a certainty for any individual dog.
Symptoms
A mast cell tumor can develop anywhere on or under the skin and looks highly variable: from a small, round, hairless lump to a red, swollen or open (ulcerated) area. Some tumors remain largely unchanged for months, while others become noticeably larger within weeks. A striking feature is that the tumor can fluctuate in size, sometimes even from day to day: touching, rubbing or temperature changes can cause the mast cells to release their granules (degranulation), making the area suddenly redder, thicker or more sensitive. In tumors that release a lot of these substances, a dog can also show more general signs, such as reduced appetite, vomiting, lethargy or dark stools from irritation of the stomach or gut lining. Because a mast cell tumor cannot always be told apart from a harmless fatty lump (lipoma) by feel, veterinary assessment of any new lump is advisable.
When to see a veterinarian?
Have any new lump or swelling on your dog assessed by a veterinarian within a reasonable time, even if it looks small or unremarkable. Do not wait if a lump grows quickly, changes color, opens up or starts bleeding, or if your dog shows clear discomfort around the area. Also see a veterinarian if your dog, alongside a known or suspected mast cell tumor, shows reduced appetite, vomiting, lethargy or noticeably dark stools: this can indicate effects from substances released by the tumor and deserves timely assessment.
How is it diagnosed?
The first step is usually a fine needle aspirate of the lump, in which cells are examined under a microscope. Mast cells are often readily recognizable by their characteristic granules, so this test can quickly confirm a strong suspicion. After surgical removal, the tissue is routinely sent to a pathologist for further microscopic examination, which determines the tumor's degree of aggressiveness (its "grade"). With a higher grade, a larger tumor, or signs of spread, the veterinarian may recommend further tests, such as blood work, an abdominal ultrasound and sampling of the nearby lymph node, spleen or liver, to assess whether the tumor has spread. Only a veterinarian and pathologist can make this diagnosis and grading; this page cannot.
Treatment in outline
Surgical removal of the tumor with sufficiently wide margins is generally the basis of treatment for a mast cell tumor, and is often sufficient for a low-grade, completely removed tumor. With a higher grade, incomplete removal, or signs of spread, the veterinarian may discuss further treatment, such as radiation therapy, chemotherapy or a targeted tyrosine kinase inhibitor. Around surgery, a veterinarian sometimes temporarily prescribes medication against the effects of histamine, such as an antihistamine or stomach protectant, to limit discomfort caused by substances released from the tumor. Which approach fits best depends strongly on the tumor's grade, location and extent, and is determined per dog by the veterinarian.
What you can do yourself
Have new lumps assessed promptly rather than waiting, and try not to unnecessarily rub, scratch or otherwise manipulate a known or suspected mast cell tumor, as this can trigger degranulation. After surgery, follow the veterinarian's advice on rest, wound care and follow-up visits closely. Check your dog's skin regularly, especially if it is a breed with an increased risk, so a new tumor is noticed early. None of this replaces veterinary guidance or treatment.
Prevention and responsible breeding
There is no proven way to prevent a mast cell tumor in an individual dog. Because breed sensitivity points to a hereditary component in some cases, responsible breeding can help: exercising caution about further breeding with animals that have had a mast cell tumor themselves, especially at a higher grade or a young age at diagnosis. For the individual owner, early recognition of a new lump remains the most important way to prevent the condition from worsening.
Living with mast cell tumors
Dogs that previously had a low-grade mast cell tumor can often lead a normal life after complete removal, although periodic skin checks remain wise, since new, unrelated tumors can develop. In breeds that more often develop multiple tumors, such as the Shar-Pei or the Pug, regular checks by the owner and follow-up with the veterinarian are especially important. With a high-grade or spread tumor, the condition can have more impact on life expectancy and quality of life; the veterinarian or a specialized oncologist can best estimate the outlook for your dog, as this varies strongly by grade, location and individual situation.
Frequently asked questions
Is a mast cell tumor in dogs always malignant?
Not by definition: the degree of aggressiveness varies strongly per tumor and only becomes clear after microscopic examination by a pathologist.
Can I recognize a mast cell tumor myself by how it feels?
No, a mast cell tumor can closely resemble a harmless fatty lump or other benign swelling; only examination by a veterinarian can provide certainty.
Is surgery always necessary?
For most mast cell tumors the veterinarian advises surgical removal, but the exact approach depends on the grade, location and health of your dog.
Can mast cell tumors come back?
A tumor at the same site can return if not all tissue was removed, and a dog can also develop a new, unrelated tumor at a different site; periodic checks therefore remain important.
Conclusion
Mast cell tumors are the most common skin tumor in dogs, with behavior that can range from mild to aggressive. Certain breeds, such as the Boxer, Shar-Pei and Golden Retriever, have an increased risk, but the tumor can develop in any dog. Early assessment of every new lump, followed by targeted testing and, where needed, surgical removal, gives the best outlook. For low-grade, completely removed tumors the prognosis is generally favorable; for high-grade or spread tumors, the veterinarian determines the best approach together with you.
Finally
Finally: this article does not replace a veterinary visit. Fidello does not provide diagnoses or prescribe treatments. If in doubt, in case of persistent symptoms or acute signs, a veterinarian is always the right next step.