Use of Photodynamic Therapy Against Squamous Cell Carcinoma in a Rose-Ringed Parakeet (Psittacula krameri)
Abstract
A 5-year-old female African rose-ringed parakeet (Psittacula krameri) presented with an ulcerated mass in the medial post-patagial area of the right wing. Biopsy specimens of the mass demonstrated a well-differentiated squamous cell carcinoma. Photodynamic therapy (PDT) resulted in tumor cell necrosis and initial reduction in tumor burden, but complete remission was not achieved.
PDT utilizes an intravenous photosensitizing agent, in this case hexyl ether pyropheophorbide-a (Photochlor, Roswell Park Cancer Institute, Buffalo, NY, USA), that is subsequently activated by a diode laser. Upon activation with the light source, cytotoxic oxygen radicals are generated photochemically and destroy neoplastic cells. The particular wavelengths of light used in PDT depend upon the photosensitizing agent used and the reported response with various neoplasms.1
One injection of Photochlor (0.3 mg/kg IV) was administered into the basilic vein 18 hours prior to activation. A diode laser fitted with a 400-µm microlens filter was used to deliver 665 nm of light to the affected tissue. Although tumor cell necrosis and reduction in tumor burden were documented, complete remission was not achieved after five courses of PDT.
Based on this and other avian cases,2,3 it appears that photodynamic therapy in avian species against squamous cell carcinoma using protocols modeled after canine, feline and human PDT protocols may not be useful. We hypothesize that differences in light penetration, photosensitizing agent pharmacokinetics, and wound healing properties in avian species necessitate alteration of PDT protocols if this treatment modality is to be effective in avian oncology. We suggest further investigation into either shortening the interval between injection and activation, altering the wavelength of light administered, or altering the treatment time during PDT.
Literature Cited
1. Klein, M.K., and W.G. Roberts. 1993. Recent advances in photodynamic therapy. Compendium. 15: 809–817.
2. Rosenthal, K., L. Duda, E.S. Ivey, and S.M. Hahn. 2001. A report of photodynamic therapy for squamous cell carcinoma in a cockatiel. Proc. Assoc. Avian Vet. 2001: 175–176.
3. Suedmeyer, W.K., D. McCaw, and S. Turnquist. 2001. Attempted photodynamic therapy of squamous cell carcinoma in the casque of a great hornbill (Buceros bicornis). J. Avian Med. Surg. 15(1): 44–49.