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

Lapatinib may offer effective medical management for canine vulvovaginal SCC when surgery is declined.

This case report describes the successful use of lapatinib, an oral dual tyrosine kinase inhibitor targeting HER1 (EGFR) and HER2, for the management of primary vulvovaginal squamous cell carcinoma (SCC) in an 11-year-old spayed female German Shepherd dog. Vulvovaginal SCC is an uncommon canine neoplasm, and this case is notable as surgical excision and adjuvant radiation therapy were declined by the owner, necessitating a medical management approach. Following confirmed incisional biopsy diagnosis and staging workup revealing no evidence of regional or distant metastasis, lapatinib was initiated as a sole therapeutic agent. A partial response was documented within one month of treatment initiation, with complete resolution of the primary lesion achieved by three months. The primary lesion did not recur over a one-year follow-up period, though new perivulvar cutaneous lesions developed that were not associated with clinical signs. The primary adverse effect observed was acute hepatic injury, which was successfully managed through hepatoprotective antioxidant therapy and intermittent treatment interruption, ultimately allowing continued lapatinib administration. This case suggests that lapatinib may represent a viable medical treatment option for canine vulvovaginal SCC when surgical or radiation therapy is not pursued, while highlighting the need for hepatic monitoring during treatment. Further prospective studies are warranted to evaluate efficacy, optimal dosing protocols, and long-term outcomes in larger patient populations.

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