Intramuscular mast cell tumors in 7 dogs.

Mast cell tumors (MCTs) are commonly encountered in dogs and have been reported in cutaneous, conjunctival, oral mucosal, and gastrointestinal locations, but not in an intramuscular location. Medical records at 2 referral centers in the UK were examined to find cases of MCTs in this location. Seven dogs were identified as having an intramuscular MCT by a combination of fine-needle aspirate cytology and computed tomography or ultrasound. None of the dogs had evidence of local lymph node metastasis. Six dogs had no evidence of distant metastasis and surgery was carried out as the primary treatment option. Three of those dogs also had adjunctive chemotherapy due to a high Ki67 value or high mitotic index. All 6 dogs that had had surgery were alive at follow-up with a minimum elapsed time of 7 months. One dog had a course of chemotherapy due to the location, size, and evidence of biological activity of the tumor and died 23 days afterwards. The prognosis of intramuscular mast cell tumors appears to be favorable in most cases.