HPV16 and HPV18 in genital tumors: Significantly different levels of viral integration and correlation to tumor invasiveness

The integration of the high-risk HPV16 and HPV18 types into the cell genome is considered an important step in malignant transformation. The relationship between the physical status of the virus and clinical/pathological parameters was studied by type-specific and multiplex PCR for E6, E2, and E1 sequences in 86 genital tumors from different sites, consisting of 69 invasive carcinomas (including 5 microinvasive carcinomas), 9 carcinomas in situ, 6 severe dysplasias, and 2 moderate dysplasias. Forty tumors contained HPV16 (46.6%), 7 HPV18 (8.1%), and 39 both viruses (45.3%). HPV16 DNA was found either as pure integrant (35.4%), or pure episome (36.7%), or a mixture of both (27.8%). Conversely, all 46 lesions containing HPV18 showed pure integrated forms. The physical status of both types was not related to the tumor site, the tumor/node/metastasis stage, or the histological differentiation grade of the invasive carcinomas. HPV16 integration was significantly associated with invasiveness. Interestingly, in double infections when HPV16 coexisted with HPV18, its genome was found more frequently in episomal form than in single infections where, conversely, it was mostly integrated (P <0.0001), suggesting a sort of competition for cell integration sites. The complete HPV18 integration, even in preneoplastic lesions, indicates a different behavior in genital transformation compared with HPV16 and may reflect a major aggressiveness of this viral type. In conclusion, virus typing in conjunction with the evaluation of the integration status may provide a better prognostic evaluation together with an improved diagnosis.