P16INK4A Immunohistochemistry is Superior to HPV in Situ Hybridization for the Detection of High-risk HPV in Atypical Squamous Metaplasia

In situ hybridization (ISH) assays for high-risk human papillomavirus (HR-HPV) and immunohistochemical (IHC) assays for surrogate markers such as p16 can be useful in detecting HR-HPV in cervical dysplasia, but the use of these markers in problematic cervical biopsies has not been well-established. We evaluated 3 chromogenic ISH assays (Ventana INFORM HPVII and HPVIII and DakoCytomation GenPoint) in conjunction with p16 IHC and HPV polymerase chain reaction in a study set consisting of 12 low-grade squamous intraepithelial lesions, 16 high-grade squamous intraepithelial lesions, and 30 benign cervix samples. A test set of 28 cases of atypical squamous metaplasia were also evaluated withVentana HPVIII ISH and p16 IHC. In the study set, the sensitivity of the DakoCytomation ISH assay (which detects HPV subtypes 16, 18, 31, 33, 35, 39, 45, 52, 56, 58, 59, and 68) was similar to the Ventana HPVII assay but less than that of the Ventana HPVIII ISH assay (both of which detect HPV subtypes 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, and 66) and less than p16 IHC (55.6% vs. 53.6 vs. 69.2% vs. 82.1%). All HPV ISH assays exhibited 100% specificity. p16 reactivity consisted of 2 patterns: focal strong and diffuse strong. Because focal strong p16 reactivity was identified in benign squamous epithelium (6.7% cases) and dysplastic epithelium, it was considered an equivocal result and only diffuse strong reactivity was considered to be specific for the presence of HR-HPV. In the squamous intraepithelial lesions study set, the difference in sensitivity between Ventana HPVIII ISH and p16 was not statistically significant. However, in the atypical squamous metaplasia test set cases, p16 reactivity (focal strong and diffuse strong) was significantly more sensitive than Ventana HPVIII ISH in correlating with the presence of human papillomavirus as detected by polymerase chain reaction (83.3% vs. 33.3% P=0.004). Because focal strong p16 reactivity is less specific, cases with this staining pattern are considered atypical and require further evaluation by other means. Overall, p16 IHC is considered the best candidate for the initial assessment of cervical biopsies that are histologically indeterminate for dysplasia given its wide availability, comparative ease of interpretation, and high sensitivity and specificity.