A tonsillar squamous cell carcinoma in a 6-year-old male Cocker Spaniel

The following are histopathology (H&E) sections from a tonsillar mass and an enlarged ipsilateral retropharyngeal lymph node.

Fig 1. An H&E section from the tonsil: the tonsil is infiltrated and effaced by nests and interconnecting islands of neoplastic squamous epithelial cells which display occasional keratin pearl formation (arrow).
Fig 2. An H&E section of the retropharyngeal lymph node: the subcapsular cortex and sinuses are extensively infiltrated by a similar neoplastic infiltrate to that present in the tonsil.
Fig 3. A higher magnification of the neoplastic infiltrate in the lymph node confirming metastatic squamous cell carcinoma.

Final Diagnosis

Tonsillar squamous cell carcinoma with metastasis to the retropharyngeal lymph node


Squamous cell carcinomas affecting the tonsil typically arise from the tonsillar fossa epithelium. The majority of tonsillar squamous cell carcinomas metastasise early with spread to the regional lymph nodes and distant sites including lungs, liver, kidneys, spleen and bone. The retropharyngeal lymph nodes are typically first affected, followed by parotid, submandibular and prescapular lymph nodes in the later stages. Because of their large size, metastatic lesions are often mistaken for the primary tumour and therefore it is important to check the oral cavity (paying particular attention to the tonsils) when a squamous cell carcinoma is diagnosed in the neck region of a dog for example.