Microscopic description and IHC:
The mass is composed of diffuse cellular infiltrate of non-cohesive cells, resembling the look of lymphoma. The cells are pleomorphic, with indistinct cell margins (syncytial), and are admixed with mixed inflammatory cells.
Immunohistochemical stains for AE1/3, CK5/6, p40, HMWK, and SOX10 are positive. S-100 shows patchy weak positivity. CK7, synaptophysin, chromogranin, and p16 are negative. CISH for EBER is positive.
Discussion:
Nasopharyngeal carcinoma is the most common cancer in the nasopharynx. It is most common in South East Asian, Northern Africa, and others. It can occur in children and adults. The causes are a combination of genetic predisposition, environmental factors, and Epstein-Barr Virus (EBV).
The World Health Organization has classified nasopharyngeal carcinoma into three types: 1) keratinizing squamous cell carcinoma, not significantly associated with EBV and usually in older ages; 2) nonkeratinizing nasopharyngeal carcinoma have a stratified or pavimented arrangement and well-defined cell borders; 3) nonkeratinizing nasopharyngeal carcinoma, which shows syncytial appearance with indistinct cell borders in a dense background of inflammatory cells. This variant is also the most common type and has the strongest association with EBV.
The malignant cells are usually positive for keratin, EMA, and occasionally CEA. Dendritic cells can be present and they are S100 positive.