In this study, the correlations of factors with Epstein-Barr virus (EBV)-association were investigated in 50 patients with nasopharyngeal carcinoma (NPC), 61 with oropharyngeal carcinoma (OPC), and 55 with hypopharyngeal carcinoma (HPC) in Okinawa and Osaka prefectures in Japan. The incidence of pharyngeal carcinoma in Okinawa was previously found to be higher than that in Osaka; the incidence of OPC was approximately 6 times higher and that of HPC was two times higher. The EBV genome was detected in the tumor cells of the present patients; 83% of the Okinawa and 92% of the Osaka NPC patients. The EBV genome was not detected in OPC or HPC. A univariate analysis showed that sex, the location of the tumor, histology, and the degree of lymphocytic infiltration correlated with the EBV-positive rate. A multivariate analysis revealed that only the location of the tumor was independently correlated with the EBV-positive rate. Histology and tumor size were factors affecting the prognosis of the patients with NPC. The NPC of poorly differentiated type frequently showed the EBV genome, and NPC with lymphocytic infiltration showed a more favorable prognosis compared to the other NPC types. These findings suggest that latent genes of EBV expressed in cancer cells might trigger a cytotoxic T cell reaction against the cancer.
Key words: Epstein-Barr virus -Pharyngeal carcinoma -EpidemiologyEpstein-Barr virus (EBV), a herpesvirus which can infect lymphocytes, was originally discovered in cultured lymphoblasts from the African type of Burkitt's lymphoma in 1964.1) An oncogenic role of EBV in the development of B cell lymphoma and nasopharyngeal carcinoma (NPC) was subsequently suggested.2) Recent studies have shown the presence of EBV sequences in carcinoma cells of thymic, 3) gastric, 4) salivary gland, 5,6) and lung cancers.
7)The pharyngeal space is divided into three parts; the nasopharynx, oropharynx, and hypopharynx. The nasopharynx is covered with pseudostratified respiratory epithelium, and the oropharynx and hypopharynx are covered with stratified squamous epithelium. The naso-and oropharynxes have well-developed lymphoid tissue, i.e., Waldeyer's ring, whereas the hypopharynx is devoid of lymphoid tissue. The association of EBV with NPC is well-known, and it has been reported that EBV-associated NPC usually have poorly differentiated morphology accompanied by severe lymphoid cell infiltration, forming a lymphoepitheliomatous lesion. It is not yet evident whether oropharyngeal and hypopharyngeal carcinomas (OPC and HPC), especially those of the poorly differentiated type, are EBV-associated.We recently reported a much higher frequency of sinonasal lymphoma in Okinawa prefecture compared to Osaka in Japan, and we showed that the majority of these lymphomas were associated with EBV.8) The incidence of pharyngeal carcinoma in Okinawa was also found to be higher than that in Osaka; the incidence of OPC is approximately 6 times higher and that of HPC is two times higher in Okinawa. 9) In the present study, we investigated wh...