Canine Intramuscular Mast Cell Tumor in the Biceps Femoris Muscle: A Case Report

Mast cell tumors (MCT) are the most common malignant cutaneous tumors in dogs, but there is very little information on intramuscular MCT. Here we report a case of a surgically treated canine MCT occurring in the biceps femoris muscle. An 11-year-old spayed female labrador retriever was presented with an intramuscular mass 5.7 cm in greatest diameter located in right biceps femoris muscle. Partial resection of the biceps femoris muscle including a mass and ipsilateral popliteal lymphadenectomy were performed. The pathohistological diagnosis was MCT with incomplete surgical margin and which were detected for mutations in exons 9 of the c-kit gene. On day 8 after surgery, the dog underwent revision surgery as removal of wider area surrounding the original site, but tumor cells were not detected histologically in the re-excised tissues. No recurrence or metastasis was observed until death on 692 days after first surgery. This case indicate that partial resection of the muscle may be a treatment option for intramuscular MCT.