A 38-year-old Southern white rhinoceros (Ceratotherium simum simum) developed a focal conjunctival lesion on the left sclera that grew into a proliferative mass (2-cm diameter) over 8 weeks. Through positive reinforcement training, topical proparacaine was utilized to biopsy the mass. Histopathology consisted of polypoid hyperplastic conjunctivitis with considerable dysplasia. Treatment with bevacizumab (Avastin® 25 mg/ml, New England Compounding Center, Framingham, MA, USA; 2.5 mg intralesionally with 30-ga needle once) resulted in rapid shrinkage and complete resolution within 7 weeks.
A 20-year-old Pacific walrus (Odobenus rosmarus divergens) developed a focal, rapidly growing gingival mass (1.5-cm diameter) lateral to the most rostral right mandibular cheek tooth. Biopsies obtained using training and topical lidocaine revealed ulcerated granulation tissue with gingivitis. Treatment with enrofloxacin (50 mg intralesionally) and topical betadine and gentamicin resolved the gingivitis, but the mass remained. Treatment with bevacizumab (5 mg intralesionally) produced minimal effect; an additional two doses (5 mg) were administered into two areas of the mass and repeated at 2 weeks. Although complete resolution was not achieved, the mass was reduced to less than 0.5 cm in diameter.
Bevacizumab, an anti-angiogenic compound, prevents neovascularization via inhibition of vascular endothelial growth factor. It is approved to treat metastatic or non-resectable colorectal, pulmonary, and mammary neoplasia and used in ophthalmology to treat neovascular macular degeneration.
In both cases, partial to complete resolution was achieved with no deleterious effects. Intralesional bevacizumab should be considered as a potential treatment for non-resectable or recurring masses.
The authors thank the veterinary staff, curators, and keepers of the Toledo and Indianapolis Zoos for their assistance in the care and management of the animals in this report.