Prevalence and expression of human papillomavirus in tonsillar carcinomas, indicating a possible viral etiology

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Abstract
The presence of human papillomavirus (HPV) DNA was assessed in biopsies of tonsillar carcinomas (n = 10) and cases of tonsillitis (n = 7), serving as controls, by general‐primer‐mediated PCR (GP‐PCR). All carcinomas appeared HPV‐positive, whereas all cases of tonsillitis were HPV‐negative. Additional type‐specific PCR for HPV 6, 11, 16, 18, 31 and 33 revealed that 4 carcinomas contained HPV 16 DNA, 4 contained HPV 33 DNA and I contained an HPV 16/33 double infection. False positivity was excluded by additional Southern blot analysis of type‐specific PCR‐positive samples (n = 4). Further characterization of GP‐PCR products by sequence analysis revealed that 2 carcinomas contained still uncharacter‐ized HPV genotypes; one of these also contained HPV 33 DNA and one was negative by type‐specific PCR. Application of RNA PCR revealed expression of HPV 16 or HPV 33 E7 encoding spliced E6*l transcripts in all tonsillar carcinomas (n = 4) examined. Additional non‐radioactive RNA in situ hybridization performed on 3 biopsies revealed the presence of HPV 16 or HPV 33 E7 transcripts exclusively localized within the carcinoma cells, whereas stroma stained negative. These findings strongly support a role for certain HPV types in the pathogenesis of tonsillar carcinomas.