Abstract
Background:
Skin tumors frequently occur in dogs, which can arise from various layers of the skin. This case reported concomitant occurrence of mast cell tumor (MCT) and cutaneous melanoma in dogs.

Case Description:
A 14-year-old male local dog weighing 23 kg was presented to the Bali Veterinary Clinic (BVC) Animal Hospital, Indonesia, with a one-month history of a lump on the right hind limb. Clinical examination revealed a 3-cm mass in the right femoral region and three smaller nodules, each measuring 0.5-1 cm in diameter, in the ventral abdominal area. Hematology and blood biochemistry analyses showed that all parameters were within normal limits, except for a slight increase in alanine aminotransferase (ALT). Fine-needle aspiration cytology (FNAC) of the right hind limb mass showed a population of mast cells, while FNAC of the ventral abdominal nodules yielded inconclusive results because the cytological features were non-specific and did not support a definitive tumor diagnosis. Histopathological examination confirmed that the right hind leg mass was MCT, whereas the ventral abdominal masses were cutaneous melanomas. Immunohistochemical staining was performed against CD117 and COX-2. Histopathologically confirmed MCT showed CD117 focal localization in the cytoplasm and low COX-2 expression, suggesting a favorable prognosis. Surgical excision was performed with a lateral margin of 2 cm. The dog received amoxicillin as an antibiotic and tolfenamic acid as an anti-inflammatory agent postoperatively. During the recovery period, carprofen and cefadroxil were prescribed as analgesics and antibiotics, respectively.

Conclusion:
The dog fully recovered within 14 days. A one-year follow-up revealed no evidence of tumor recurrence. This case report describes the successful surgical treatment of a concomitant MCT and cutaneous melanoma.

Key words: Cytology; Histopathology; Immunohistochemistry; Skin tumors.