Evaluation of HPV testing by Hybrid Capture II for routine gynecologic screening

Based on the causal involvement of HPV in cervical cancerogenesis (1), it has been suggested to use HPV typing in cervical cancer screening programs. Indeed, HPV testing was shown to identify patients with high grade cervical intraepithelial lesions (HSIL) and cancer with higher sensitivity than cytology (2). The assays most frequently used for HPV DNA detection are the commercial Hybrid Capture Test (HC) (Digene, Silver Spring, MD) and PCR assays using various primer pairs. In contrast to PCR based assays, the HC-II test only differentiates between HR and low-risk (LR)-HPV types, but does not allow typing of individual HPVs. Nevertheless, due to the easier performance, the HC-II test may be preferred in large scale screenings by routine laboratories. To verify the suitability of HC-II for routine HPV testing in gynecologic screenings, we compared the test with a PCR assay based on MY09/11 primers. Cervical smears that have been tested for HPV DNA by HC-II in a gynecologic laboratory under routine conditions were re-tested by PCR in another laboratory. The analysis was done in a blinded fashion using a PCR assay that has been shown to reliably detect and type HR-HPVs in an inter-laboratory comparison (3). The study population consisted of 54 caucasian women aged between 21 and 74 years (mean 33.3 years, 32 patients <35 years, 22 patients ≥35 years). The results of cytologic, histologic and colposcopic investigations as well as HPV testing are summarized in Table I. Fifteen patients had evidence for HSIL by cytology or histology. HR-HPV DNA was detected by both HC-II and PCR in cervical smears from 14 of these patients. These results confirm the high sensitivity of HPV testing to detect cervical dysplastic lesions described in previous studies (2). On the other hand the usefulness of HPV testing with respect to directing decisions about clinical management was reported to be limited by HR-HPV positive results in LSIL and normal specimens. We also detected HPV DNA in patients with LSIL or without cervical dysplasia. Using HC-II the HR-HPV probe was reactive in seven (78%) of nine LSIL and in eight (27%) of 30 normal cervical smears. The rate of HR-HPV positives detected by PCR was 33% for LSIL and 13% for normal smears. Thus HC-II appeared to be less specific for identification of dysplastic or neoplastic lesions. Concordant results of HPV detection by PCR and HC-II, irrespective of HPV type, were obtained in all cases of HSIL. Complete agreement of both tests was found in 73% of HSIL. The rest of these specimens showed partial agreement (same result of HR-HPV testing, but different result of LR-HPV testing). In normal smears and LSIL concordant results were found in only 50% and 44%. In part these discrepant results may be due to cross reactions of the HR-HPV-probe with HPV types not considered in the test. In fact PCR analysis of some of the HC-II-HR-HPV-positive LSIL or normal smears revealed the presence of HPV types 34, 53, 66 and a putatively novel HPV sequence HPVXS4. The oncogenic potential of these HPVs is not known exactly, but seems to be rather low. In a recent paper from the ALTS-group it was also suggested that the HC-II-HR-HPV probe reacts with other HPV types of low or unknown oncogenic potential (4). Although HPV-positive normal smears may represent latent infections that could be an early indicator for the development of cervical disease (5), some of the HC-II-HR-HPV positive LSIL or normal lesions are likely to depend on cross reaction with yet uncharacterized HPV types. In our opinion, the specificity of HC-II for HR-HPVs must be improved in order to reduce the number of positive results in normal smears. Based on our findings, PCR is more reliable than HC-II for HPV testing in gynecologic cancer screening.