Tonsillar Squamous Cell Carcinoma in a Dog

Therapeutic Effects of Carboplatin Alone and Adjuvant Piroxicam

Abstract

Background: Primary tonsillar neoplasia in dogs is rare, and among these tumors, tonsillar squamous cell carcinoma (SCC) is of particular concern because of its aggressive biological behavior, high metastatic rate, and generally poor prognosis. Reported treatment strategies for this include surgery, chemotherapy, radiation therapy, and non-steroidal anti-inflammatory drugs (NSAIDs). However, the optimal therapeutic approach remains undefined, and data regarding the efficacy of systemic chemotherapy as a single modality are limited. This report describes the clinical course and outcome of a dog with advanced tonsillar SCC managed with carboplatin in combination with adjuvant piroxicam. 

Case: A 14-year-old castrated male Mongrel dog was evaluated for anorexia, lethargy, and bilateral cervical masses. Physical examination and ultrasonography identified marked enlargement of the bilateral medial retropharyngeal and right submandibular lymph nodes (LNs), as well as a hypoechoic nodule in the spleen. Fine needle aspiration of both the lymph nodes and the splenic lesion revealed malignant epithelial cells. Computed tomography further demonstrated a right tonsillar mass consistent with a primary tumor, supporting a diagnosis of tonsillar SCC with concurrent lymph node and splenic metastases. The patient underwent 7 cycles of carboplatin chemotherapy (179.4-207 mg/m2, intravenous, every 3 weeks) administered concurrently with oral piroxicam (0.3 mg/kg, once, daily). Following the initial cycle, the dog exhibited rapid improvement in clinical signs, including resolution of anorexia, lethargy, and weight loss. Serial physical examination and imaging demonstrated a partial response, characterized by substantial reduction in the cumulative size of metastatic lymph nodes and complete resolution of splenic metastasis although the primary tonsillar lesion remained stable in size. After the 7th carboplatin cycle, the dog developed severe neutropenia accompanied by gastrointestinal signs, prompting discontinuation of chemotherapy at the owner’s request. Palliative management with piroxicam alone was continued, but progressive lymphadenopathy and worsening clinical symptoms ensued. The patient was transitioned to hospice care and died at home 53 days after cessation of chemotherapy, surviving 208 days from the time of diagnosis. 

Discussion: This case highlights several important clinical considerations in the management of canine tonsillar SCC. Although regional lymph node involvement is common, the occurrence of splenic metastasis is rare, underscoring the importance of comprehensive diagnostic staging in patients with suspected primary tonsillar tumors. While multiple treatment modalities are available, including surgery and radiation therapy, no single strategy has been shown to consistently improve long-term outcomes, particularly in cases with advanced local invasion or metastasis where local therapies are of limited benefit. In this patient, the combination of carboplatin and piroxicam achieved meaningful clinical improvement, prolonged survival, and control of metastatic lesions in the absence of surgery or radiotherapy. These findings suggest that carboplatin, when administered alongside NSAID therapy, may provide therapeutic benefit in selected cases of advanced canine tonsillar SCC. Further studies are warranted to establish the efficacy, safety, and optimal role of chemotherapy and adjunctive agents in the management of this aggressive neoplasm.

Keywords: dogs, tonsillar squamous cell carcinoma, carboplatin, chemotherapy, piroxicam.