Topical Mitomycin C Chemotherapy After Surgical Resection of Conjunctival Amelanotic Melanoma in a Dog

OBJECTIVE: To describe the clinical course and outcome of adjuvant topical mitomycin C (MMC) therapy following incomplete resection of a conjunctival amelanotic melanoma in a dog. ANIMALS STUDIED: A 15-year-old spayed-female Shih Tzu presented with a conjunctival mass in the right eye (OD). METHODS: Ophthalmic and physical examinations, along with computed tomography results, confirmed that the tumor was confined to the conjunctiva and showed no systemic metastases. However, the mass had spread throughout the bulbar conjunctiva and third eyelid OD. A conjunctival mass involving the bulbar conjunctiva and the bulbar surface of the third eyelid of the OD was surgically debulked after the owners declined exenteration. RESULTS: Histopathology and immunohistochemistry confirmed malignant amelanotic melanoma with incomplete surgical margins. Adjuvant topical chemotherapy with 0.04% MMC ophthalmic solution was administered four times daily for one month following conjunctival healing. During topical MMC therapy, superficial corneal epithelial defects and conjunctival hyperemia developed, which resolved after discontinuation of the medication. Reduced tear production was noted during long-term follow-up and was managed with topical cyclosporine. No clinical evidence of local tumor recurrence was observed during the 14-month postoperative follow-up period, based on physical and ophthalmic examinations. CONCLUSION: In this case of conjunctival amelanotic melanoma with incomplete surgical excision, adjuvant topical MMC therapy was associated with the absence of clinically detectable local recurrence during long-term follow-up. Topical MMC may represent a potential globe-preserving adjuvant treatment option in selected cases of incompletely excised conjunctival melanoma; however, further studies are required to better define its efficacy and safety.