Squamous cell carcinoma of the oral cavity in an infant cynomolgus monkey.

Squamous cell carcinoma was observed in the oral cavity in a one-year-old male cynomolgus monkey. Histopathologically, the tumor consisted of various shaped cells and its assemblies infiltrated into the surrounding connective tissues. Although no obvious metaplastic keratinized cancer pearls were found in the tumor cells, the intercellular bridges were observed. Immunohistochemically, tumor cells were stained with anti-keratin, but not with anti-vimentin. On virological examinations, no papilloma virus antigen or Epstein-Barr Virus small mRNA could not be detected. Under the electron microscope, incomplete tonofibrils and desmosomes in the cytoplasm and microvillus of the cell membrane were observed, suggesting a malignancy or low differentiation of the tumor cells in the present case. This is the first case of squamous cell carcinoma observed in very young macaques, to our knowledge.