This week's New England Journal of Medicine (357:1579-88, 2007) reports a very important study that looks at the performance of HPV molecular testing for screening for grade 2 and 3 (i.e., high-grade) cervical intra-epithelial neoplasia. The population consisted of over 10,000 women aged 30-69 in Canada with good access to health care. Sensitivities for HPV and cytology were 94.6% and 55.4%, respectively. Specificities were 94.1% and 96.8%.
Cervical cancer screening by the use of the Pap smear has been one of the best examples of a successful cancer screening program in history. With current practice, it's common that HPV testing is used to clarify cases of ASCUS (identified by cytology/cytopathology) rather than as a primary screening technique. This study (and others) suggests that HPV testing could be a primary screening modality, although more data are needed to reach that conclusion with certainty.
From a laboratory perspective, screening programs need high sensitivity, and the difference between molecular HPV testing and cytology is striking. On the other hand, there is variation in the number of HPV types that can be detected by different molecular methods and the method used in this study may not be the most sensitive. Different assays have different sensitivities and specificities (see J Clin Micro 45:2130-7, 2007 for example). This study demonstrates that in vitro molecular testing can, in certain situations, be a viable alternative to microscopy. This last point emphasizes the need for pathologists to be closely involved with molecular pathology and its implementation in hospital laboratories or they risk being marginalized in the changing diagnostic landscape. For many cytology technicians and cytopatholgists, Pap testing (or one of its liquid counterparts) is the major professional activity of the daily workload. A widespread change from morphology to in vitro testing for HPV could pose the possibility of sudden and substantial disruptions to professional activities.
