Marginal Resection and Acridine Orange Photodynamic Therapy in a Cat with Recurrent Cutaneous Malignant Melanoma

If a tumor cannot be completely resected, an adjunctive treatment modality is recommended to prevent local recurrence. One treatment option is intraoperative photodynamic therapy (PDT), which uses the reagent Acridine orange (AO). A 9-year-old domestic short-haired castrated male cat previously underwent surgical resection of a malignant melanoma at the left upper eyelid four times at another veterinary hospital. The tumor was resected with a 1 cm margin laterally, but the caudal margin contacted the cranial bone. AO-PDT was performed to control the residual tumor cells. At 9 months postoperatively, local recurrence was detected, and AO-PDT and surgical resection was repeated. At 16 months postoperatively, the cat died, but tumor recurrence was not detected at the original site. There were no adverse effects from the AO-PDT detected at the surgical site at any time during followup. This case report suggests that AO-PDT may be useful in combination with marginal resection of malignant tumors in cats, especially when radiotherapy is not performed.