Complete Response to the Combination of Immunotherapy and Targeted Therapy in Stage IV Nasal Adenocarcinoma of a Dog: A Case Report.

Nasal adenocarcinoma is the most common nasal tumour in dogs, typically presenting with epistaxis, purulent discharge and sneezing. This malignancy often leads to local tissue invasion and, in advanced stages, neurologic symptoms. Without treatment, the prognosis of affected dogs is poor. While radiation therapy remains the standard treatment, its limited availability in some regions presents significant challenges. As a result, alternative treatments, including immunotherapy and targeted therapy, are gaining attention as viable options for improving outcomes in affected dogs. In March 2022, a 12-year-old uncastrated male West Highland white Terrier with a 1-month history of chronic sneezing and unilateral epistaxis was referred for nasal tumour evaluation. Histopathologic examination revealed a nasal adenocarcinoma. Computed tomography indicated a 1.73 cm irregular soft tissue mass in bilateral nasal passages and frontal region with peripheral osteolysis but no local lymph node metastasis. The dog first received seven doses of anti-programmed death-1 (PD-1) monoclonal antibody (mAb) (MP-001); after progression at 3 months (Day 91), we added seven doses of toceranib phosphate (Palladia) to the regimen. Remarkably, this treatment led to radiographic complete response (according to Veterinary Cooperative Oncology Group [VCOG] criteria), with the dog surviving 638 days from the initial diagnosis. This single case highlights the potential efficacy of combining anti-PD-1 mAb with Palladia in treating advanced nasal adenocarcinoma in dogs. Given the limited treatment options and poor prognosis for this aggressive cancer, this report suggests further investigation into such combination therapies may offer a promising alternative to conventional treatments like radiation in the future.