Overview:

The treatment of choice for multiple low-grade mast cell tumours (MCTs) in dogs is surgery. Managing multiple MCT surgeries can be challenging and distressing for both owners and veterinarians. I've encountered cases where a single dog underwent up to 35 MCT removals in one surgery and over 50 throughout its lifetime. It can be disheartening to perform multiple surgeries within a year or find new tumours shortly after. This guide covers surgical options, the use of intralesional triamcinolone, and considerations for chemotherapy and Palladia. Learn about the risks of recurrence and pre-surgical recommendations to ensure optimal care for your canine patients.

Surgical Treatment:

While it may not be the preferred option for owners or veterinarians, surgery remains the most effective treatment for multiple low-grade MCTs, provided they are not recurrences or metastases. If each tumour is low-grade, with a low mitotic count and non-aggressive characteristics, surgical removal is likely curative, with very low risks of recurrence and metastasis. Typically, no further adjuvant therapies are required.

Intralesional Triamcinolone:

For dogs with small MCTs where surgery or general anaesthetic is not an option, intralesional triamcinolone injections can be considered. This involves administering 1-2 mg of triamcinolone per cm of MCT. For small MCTs, this typically involves 0.5 or 1 mg triamcinolone using a 25 G or 23 G needle. The injection can be undiluted or diluted with a small volume of 0.9% NaCl directly into the MCT. It's typically injected in several areas of the MCT, although small lesions may make this challenging. This procedure can be uncomfortable, so sedation is often recommended. Assess the lesion one to two weeks later, and if no response is observed, try one more injection before considering alternative treatments.

Triamcinolone is a glucocorticoid with 4-5 times the potency of hydrocortisone and no mineralocorticoid activity. In a study of 23 dogs with MCTs larger than 0.5 cm, the response rate was 67%, with some dogs achieving complete remission. While well-tolerated, potential adverse events include local haemorrhage and gastrointestinal ulceration. Owners should be aware of these possibilities. The aim is for complete remission; if not achieved after two injections, consider other options.

During treatment, administering antihistamines and omeprazole is recommended, ideally a few days before treatment, and continuing until complete remission is achieved.

Chemotherapy and Palladia:

Although some veterinary oncologists recommend chemotherapy or Palladia for managing mast cell tumours (MCTs), current evidence does not support their use in preventing additional MCTs. These treatments are generally reserved for cases involving high-grade MCTs, metastasis, or when palliative care is needed due to an excessive number of tumours that make further surgical resection impractical.

Risk of Recurrence:

Dogs with one MCT have a 20% chance of developing more. Anecdotally, I believe the risk may be higher.

Pre-Surgical Considerations:

Before surgery, consider neoadjuvant prednisolone at 1 mg/kg PO q24h for a maximum of 7-10 days to shrink the tumours and facilitate skin closure. Administer concurrently with omeprazole (0.7-0.8 mg/kg PO q12h) and loratadine (0.5 mg/kg PO q24h) to reduce the risk of MCT degranulation. Discontinue these medications once all macroscopic/gross MCT disease is successfully removed.

Alternative Options:

If staging reveals metastasis or the owners decline surgery in the future, chemotherapy or other oral anticancer options can be considered for palliative care. Response rates for chemotherapy and Palladia® vary between 40-70%, with median survival times of 3-12 months. If this approach is necessary, please inform me, and I can provide detailed information on Palladia® and chemotherapy options.

Veterinarians, if you have any questions or need assistance with a case, please get in touch with us.