Fluorescent Light Energy ( <scp>FLE</scp> ) as an Adjunctive Therapy in Canine Cutaneous Epitheliotropic Lymphoma ( <scp>CTCL</scp> )

BACKGROUND: Fluorescent light energy (FLE; Phovia, Vetoquinol) is a photobiomodulation therapy that promotes healing and reduces inflammation. Cutaneous epitheliotropic lymphoma (CTCL) is a neoplastic skin disease with limited treatment options. Although FLE is not considered genotoxic, its use in neoplastic conditions is off-label. HYPOTHESIS: To assess the safety and clinical effect of FLE as an adjunctive treatment for canine CTCL. ANIMALS: Eight client-owned dogs were diagnosed with CTCL via biopsy analysis and immunohistochemical analysis. MATERIALS AND METHODS: Each dog had one CTCL lesion treated with FLE with a lesion serving as a vehicle-control. Treatments were administered weekly for 6 weeks, followed by 3 months follow-up. Focal nodular lesions were assessed weekly using Response Evaluation Criteria of Solid Tumours (RECIST), while diffuse lesions were evaluated using the Canine Epitheliotropic Lymphoma Extent and Severity Index (CELESI). Owner-perceived efficacy and quality of life were assessed using the Owner Global Assessment of Treatment Efficacy (OGATE) and a quality-of-life (QoL) survey. RESULTS: No statistically significant differences in estimated marginal means were observed between sites at any time point (p > 0.05). Within-subject analyses suggested more favourable lesion progression at FLE-treated sites, and 75% of RECIST-evaluated FLE lesions maintained stable disease. Diffuse FLE-treated lesions demonstrated clinical severity reductions of ≤ 35.3%. Over 66% of owners rated treatment response as 'fair' to 'excellent' on the OGATE. One dog was withdrawn at Week 3 as a consequence of unrelated worsening. CONCLUSIONS AND CLINICAL RELEVANCE: FLE appears to be a safe adjunctive therapy for canine CTCL, although statistically significant treatment effects were not demonstrated.