Use of the dual tyrosine kinase inhibitor lapatinib for the treatment of vulvovaginal squamous cell carcinoma in a dog.

Vulvovaginal squamous cell carcinoma (SCC) is an uncommon neoplasm in dogs. An 11-year-old female spayed German Shepherd dog presented with a history of excessive peri-vulvar grooming and a 3 cm × 3 cm irregular mass involving the vagina and vulva. Incisional biopsy confirmed a diagnosis of primary vulvovaginal SCC. Abdominal ultrasonography and thoracic radiographs indicated no evidence of systemic or regional metastasis. Surgical excision and adjuvant radiation therapy were declined, and the patient was treated with lapatinib, an orally administered dual tyrosine kinase inhibitor. Treatment resulted in a partial response within 1 month and complete resolution of the primary lesion within 3 months. No recurrence of the initial lesion was observed after 1 year of treatment despite development of perivulvar cutaneous lesions that were not associated with clinical signs. Lapatinib was well tolerated but did result in acute hepatic injury that was resolved using hepatoprotective antioxidant medication and intermittent treatment cessation.