Formalin use for surgical margin control after resection of gingival fibroma in a mare

Summary
Gingival fibroma is rare in horses and is most commonly located in the rostral portion of the maxilla or mandible; however, more caudal locations have occasionally been reported. Although these lesions are benign, they have a high recurrence rate if all abnormal tissue is not completely removed. Standard treatment typically involves surgical excision, sometimes combined with adjunctive chemotherapy. In certain cases, more aggressive procedures such as mandibulectomy may be required depending on tumour size and anatomical location. However, these approaches are not always feasible due to anatomical constraints or financial limitations. This report describes the management of a gingival fibroma in a horse in which complete surgical excision was not possible. Following tumour recurrence after initial surgical debulking and local adjunctive chemotherapy using carbolatin, a second approach was performed using multiple intralesional injections of a 10% formalin solution after an additional surgical debulking. This technique resulted in progressive regression of the mass. No tumour recurrence was observed during a follow‐up period of 22 months, and only mild local adverse effects were reported. This case suggests that intralesional formalin injection may represent a simple and cost‐effective adjunctive treatment option for selected intraoral tumours in horses when conventional approaches are limited.