Mast Cell Tumors in Dogs: treatment options, palliative care, and How to know when it’s time for Euthanasia

Mast cell tumors (MCTs) are one of the most common skin cancers in dogs. They arise from mast cells, which are part of the immune system and play a role in allergic reactions. These tumors can appear anywhere on the body and vary in size and severity. Some remain localized and slow-growing, while others are aggressive and spread to organs such as the liver, spleen, or lymph nodes.

Mast cell tumors are typically diagnosed through a fine needle aspirate (FNA), where a small sample of cells is taken from the tumor and examined under a microscope. A biopsy may be performed to determine the tumor’s grade, which indicates its aggressiveness. Additional tests, such as ultrasound, blood work, and lymph node evaluation, help determine whether the cancer has spread (metastasized).

Treatment Options for Mast Cell Tumors

Treatment for MCTs varies based on the tumor’s location, grade, whether cancer has spread (metastasized), and the general health of the dog. The main options include surgery, chemotherapy, radiation, and palliative care.

Surgery
Surgery means removal of the tumor with surgery. The tumor is then often sent off for a biopsy to determine grade. Dogs with low grade tumors often have a good prognosis (meaning they live a long time after the tumor is removed). Dogs with high grade tumors have a poorer prognosis (meaning they are more likely to die from their cancer).

Pros of surgery:

• Can be a cure, especially if the tumor is low grade
• Relieves symptoms caused by the tumor

Cons:

• May not be possible in difficult locations
• Risk of recurrence if margins are not clear
• Expensive and requires anesthesia
• Patients in poor health may not be good candidates for surgery and anesthesia

For example, a 7-year-old dog with a 2 centimeter mast cell tumor on its side is a great candidate for surgery. If it is low grade, they are likely cured! A 15-year-old dog with a large tumor on the leg that cannot be removed without amputating the entire leg is likely not a good candidate for surgery.

Chemotherapy
Chemotherapy is used to treat cancer that is not confined to one location. It may be recommended for dogs who had surgery and the biopsy is high-grade (where there is concern for spread) or for dogs with known spread (metastasis).

Pros:

• Can slow tumor growth and spread, leading to a longer life
• Some types of chemotherapy are oral and can be given at home

Cons:

• There may be side effects such as vomiting, diarrhea, and lethargy
• Frequent vet visits are often required
• Not usually a cure but can prolong survival

Radiation Therapy
Radiation therapy is sometimes used to treat tumors that cannot be removed with surgery, often because they are in a place where surgery would be impossible. Radiation involves multiple visits to a specialty hospital where the patient is anesthetized and radiation is applied to the tumor.

Pros:

• Can be effective for tumors that cannot be removed via surgery
• Can sometimes provide long-term control

Cons:

• Requires numerous visits to a specialty center requiring anesthesia
• Can sometimes damage to nearby tissues
• Can be expensive and may not be widely available
• May not be completely curative

A healthy 8-year-old golden retriever with a mast cell tumor on the lip who loves going to the vet is a good candidate for radiation therapy. A 14-year-old German Shepherd who is terrified of the vet and has kidney disease may not be a good candidate for radiation.

Palliative Care Measures for Comfort

When curative treatments are not an option, palliative care focuses on maintaining the dog’s comfort and quality of life for as long as possible.

Antihistamines
Antihistamines are often prescribed to prevent mast cell tumor “degranulation” – a life-threatening complication of mast cell tumors similar to anaphylactic shock.

• Diphenhydramine (Benadryl) – Helps prevent anaphylaxis associated with mast cell degranulation
• Famotidine (Pepcid) – An antihistamine that protects the stomach lining from mast cell degranulation

Anti-inflammatories

• Steroids (e.g., prednisone) – steroids can help stabilize and sometimes temporarily shrink mast cell tumors. They can also provide some relief from inflammation.

Nausea management and appetite stimulation
Dogs with metastatic mast cell tumor that has spread internally may experience a loss of appetite, vomiting, and weight loss. Medications that may help with these symptoms include:

• Entyce (capromorelin) – An appetite stimulant that can be given daily to help your dog eat, maintain energy, and keep on weight
• Cerenia (maropitant) – An anti-nausea medication that can help with vomiting, nausea and appetite.

How to Know When It’s Time for Euthanasia

If you have a pet with metastatic mast cell tumor or a pet with a single tumor that can’t be removed and is causing quality of life issues, you may find yourself facing the decision of how to know when it’s time for euthanasia.

First, I recommend taking our quality of life quiz (https://pawsatpeace.com/quality-of-life-scale/) to help you assess your pet’s quality of life. The quiz can be taken once to give you a snapshot or multiple times to assess trends.

I also recommend keeping a daily diary of your dog’s quality of life in a journal. I recommend simply putting a smile for a good day and a frown for a bad day. The journal can also be a place where you write new memories you made with your dog each day. It is important when facing the end of life to live in the moment and cherish every single day.

Finally, I recommend giving your dog a peaceful goodbye before too much suffering has set in. If we do this, your dog’s last day can actually be a good one, and they don’t need to know the severe suffering that often accompanies end-stage cancer. When you are starting to see more bad days than good days, and they seem to have more moments they’re not feeling well rather than experiencing joy, it’s a good time to give them a beautiful send-off.

Signs it may be time to consider euthanasia:

• Tumors that are highly inflamed/bleeding frequently/causing constant licking/scratching – If your dog has a mast cell tumor that bleeds frequently, or your dog is constantly licking/scratching because a tumor is painful or itchy, and steroids and anti-histamines are no longer helping, it may be time to consider euthanasia.
• Uncontrollable weight loss, vomiting, and loss of appetite – Dogs with mast cell tumor that has spread internally will often lose their appetite, vomit, and lose weight. If appetite stimulants and nausea medications are no longer helping, it may be time to consider euthanasia.
• Recurrent severe gastrointestinal signs – if mast cell tumors degranulate they can cause sudden onset severe, often bloody, vomiting and diarrhea leading to severe dehydration and often the need for hospitalization. If this is happening repeatedly despite antihistamines it may be time to consider euthanasia so they don’t pass away in a crisis.
• Difficultly breathing – if cancer spreads to the lungs it can cause difficulty breathing. If your pet’s breathing is starting to become labored I recommend considering euthanasia. We never want our dogs to pass away from struggling to breathe if we can avoid it.
• Loss of interest in life – Consider your pet’s favorite activities – the things they live for. That may be chasing a ball, snuggling with you on a couch, sniffing around at a park. If your dog is no longer enjoying these activities, becoming more withdrawn, and interacting less with loved ones it may be time to consider euthanasia.

Conclusion

Mast cell tumor can be a scary diagnosis, but by taking certain measures, we can help our dogs enjoy a comfortable and happy life for as long as possible. If you would like more guidance and support, we offer comprehensive teleconsults with compassionate veterinarians. We will review all your pet’s medical records and history, discuss all your options, and help you formulate the most compassionate and loving plan for your family.