Epstein-Barr virus genome in thymoma and thymic lymphoid hyperplasia.

In a study of 23 consecutive thymectomies from patients with myasthenia gravis (MG), 10 (43.5%) were thymomas, 8 (34.8%) were thymic lymphoid hyperplasia (TLH), and 5 (21.7%) were normal/involuted thymuses. The incidence of thymoma in MG appears to be considerably higher in Hong Kong than in similar series from Western countries. Six patients from this group were examined for the presence of Epstein-Barr virus (EBV) genome by Southern blot, as were a thymoma from a patient without MG, a patient with TLH in the absence of MG, and 3 normal control thymuses. All 3 thymomas (2 of 2 with MG, 1 of 1 without MG), 2 of 4 TLH with MG, and 1 of 1 TLH without MG were positive for EBV genome. Thymoma should be included, along with nasopharyngeal carcinoma and malignant lymphoepithelial lesions of the salivary gland, as EBV-related epithelial tumors, all of which are prevalent in this region.