Skin depigmentation associated with toceranib phosphate in a dog

Background Drug‐induced depigmentation is frequently observed in humans undergoing tyrosine kinase inhibitor therapy, whereas it is not reported in dogs. The skin depigmentation can occur after the first week of treatment and it is reversible within a few weeks after drug discontinuation. Objectives To report the clinical and histopathological features of an episode of cutaneous adverse drug reaction associated with short term administration of toceranib phosphate. Case report An 11‐year‐old intact male Bernese mountain dog was presented for investigation of a subcutaneous mast cell tumour ( MCT ) including treatment options. The major abnormality on physical examination was a 7.5 × 10 cm subcutaneous mass located cranial to the left shoulder joint consistent with a MCT . Toceranib phosphate therapy was initiated. Fourteen days after initiating treatment, the dog presented with skin erosions near the lateral canthus of the left eye. Three weeks later there were multiple skin lesions characterized by alopecia and depigmentation involving left and right eyelids; leukotrichia of the periorbital areas and depigmentation of the nasal planum and all paw pads. Histopathological findings were nonspecific; they were supportive of vitiligo. Resolution of skin lesions was observed after stopping the toceranib phosphate therapy. Conclusion and clinical importance Based on the gross lesions, histopathological features before and after tyrosine kinase inhibitor therapy, and Naranjo score, this case was considered to be consistent with cutaneous adverse drug effects. To the best of the authors’ knowledge, this is the first report describing the clinical and histopathological features of presumed drug‐induced skin depigmentation in a dog receiving toceranib phosphate.