The Epstein-Barr virus (EBV) is consistently associated with undifferentiated nasopharyngeal carcinoma (NPC). There is, however, conflicting evidence as to whether squamous cell NPCs are also EBV-associated. Moreover, it has been proposed that other epithelial tumours, particularly thymomas and thymic carcinomas, should be included in the group of EBV-associated neoplasias. However, since the viral DNA in these studies was demonstrated only in extracted DNA, the cellular origin of the viral DNA is uncertain. We have therefore investigated 152 epithelial tumours from various sites for the presence of EBV-DNA by in situ hybridization with 35S-labelled probes. Sixty-eight of 77 undifferentiated NPCs showed an EBV-specific autoradiographic signal, thus confirming the strong association of this tumour type with EBV even in geographical areas where undifferentiated NPC is not endemic. None of eight squamous cell NPCs showed an EBV-specific signal. All of 15 carcinomas with a similar morphology to undifferentiated NPC but from different anatomic sites (thymus, tonsil, breast) were EBV-negative as were 9 thymomas, 26 squamous cell carcinomas of the palatine tonsil, and 14 cervical carcinomas. Our results therefore suggest a unique association of EBV with undifferentiated NPC and support concepts assigning different biological properties to undifferentiated NPC as compared with squamous cell NPC.

Twenty eight tonsillar carcinomas of various histological types were investigated for the presence of Epstein-Barr virus (EBV), cytomegalovirus (CMV), and human papillomavirus (HPV) types 6, 11, and 16 by in situ hybridisation using highly stringent procedures. In six cases an autoradiographic signal was obtained in the tumour cell nuclei with the HPV type 16 specific probe. As all of these cases were negative with EBVspecific probes (G Niedobitek, unpublished observations) we extended our study to other DNA tumour viruses and report here the results obtained with HPV specific DNA probes. MethodsFormalin fixed, paraffin wax embedded biopsy specimens of 28 tonsillar carcinomas were studied. Sixteen (57%) patients were male and 12 (43%) were female. The age of the patients ranged from 43 to 85 years, with a median of 66 years (table). The women were older than the men, the median ages being 70 years and 59 years, respectively. Tobacco smoking or alcohol abuse, or both, were risk factors for most of the patients (table). The tumours were graded according to WHO criteria.'4 Two carcinomas were well differentiated, 12 moderately differentiated, and 11 poorly differentiated squamous cell carcinomas. One case was an in situ carcinoma and two were lymphoepithelioma-like carcinomas with morphological similarities with undif-