Lack of Evidence of Pathogenetic Role of Epstein-Barr Virus in Thymic Lymphoid Hyperplasia and Thymomas in the Chinese Population of Hong Kong

A previous study from Hong Kong by McGuire et al. reported frequent demonstration of Epstein-Barr virus (EBV) DNA by Southern blot analysis in thymoma, thymic lymphoepithelioma-like carcinoma, and thymic lymphoid hyperplasia. This provoca tive finding, however, could not be confirmed by studies in the Western populations using the Southern blot technique and/or polymerase chain reaction to detect EBV- DNA or in situ hybridization to detect EBV encoded RNA (EBER), raising the possibility that the association with EBV may be restricted to Asians. This study was performed to clarify this issue by using a highly sensitive localization technique for EBER on a larger series from the Asian population of Hong Kong. Paraffin sections obtained from 10 cases of thymic lymphoid hyperplasia, 42 noninvasive thymomas (including one case previously reported to be EBV positive), 11 invasive thymomas, and 9 thymic carcinomas (including 5 cases of lymphoepithelioma-like carcinoma) were studied. EBER signal was not detected in the epithelial cells in any of the cases except for two cases of lymphoepithelioma-like carcinoma. In two thymomas, a few small lympho cytes (<0.1%) were EBER positive. Failure to detect EBER was not an artifact due to RNA denaturation, because preserved mRNA could be demonstrated by oligo-dT labelling in 56 of the 72 cases. Thus, the results of this study on Hong Kong Chinese are in keeping with those reported in Caucasians, and more recently in Japanese and Taiwan Chinese, in that there is no association of EBV with thymic lymphoid hyperpla sia or thymoma, and that EBV may be demonstrated in a proportion of thymic lymph oepithelioma-like carcinomas. The positive results previously reported cannot be ex plained, because the occasional EBV-carrying lymphocytes detected in rare cases of thymoma should be insufficient to give a positive EBV result by Southern blot tech nique. Int J Surg Pathol 2(1):17-22, 1994