Primary ocular surface squamous cell carcinoma (SCC) is common in horses and cattle but rarely described in dogs. Chronic keratitis, as seen in brachycephalic breeds, and use of topical cyclosporine have been hypothesized as possible triggers in corneal SCC pathogenesis in dogs. In this case, a 12-year-old male pug had a well-demarcated, central, 3-mm diameter, pale pink raised mass on the right cornea. Temporal to this lesion was a poorly demarcated 5 mm-diameter, rough, slightly raised white lesion. Severe, dense corneal pigmentation was also present diffusely on the right eye, as was moderate superficial corneal vascularization. An incisional biopsy of the central mass revealed findings consistent with corneal SCC.
The owner declined surgical excision, and the lesions were treated with 1% 5-fluorouracil ointment 4 times a day for 2 weeks. This was followed by 2 weeks with no treatment, then by another 2 weeks with treatment 2 times a day. To reduce corneal pigmentation, ongoing therapy with 2% cyclosporine was prescribed. There was no evidence of SCC regrowth on the cornea 10 months after stopping 5-fluorouracil therapy. The only complication was progression of the dense corneal pigmentation, likely secondary to the client discontinuing cyclosporine therapy. The authors concluded that 1% 5-fluorouracil potentially could be used as sole therapy for corneal SCC, although more studies are warranted.
