p16 Immuno-Cytochemistry for the Triage of ASC-US and LSILPap Cytology Cases Results from a Large Retrospective Study
KJ Denton, C Bergeron, P Klement, MJ Trunk, R Ridder. Southmead Hospital, Bristol, United Kingdom; Laboratoire Pasteur-Cerba, Cergy, France; mtm Laboratories, Heidelberg, Germany
Background: Detection of over-expression of cell cycle regulator protein p16 in cervical cytology specimens as a surrogate marker for transforming HPV infections has been described in the literature. However, there is substantial variance regarding methods used for slide preparation, staining for p16, and slide interpretation. Typically, total numbers of cases are low, and biopsy follow-up data were only reported in a few studies. We therefore evaluated the performance characteristics of p16 immuno-staining in cervical cytology specimens categorized as ASC-US or LSIL to identify women with underlying CIN2+ in a large retrospective study.
Design: 810 LBC samples (ThinPrep, Cytyc) less than 3 years old and categorized as either ASC-US (n=385) or LSIL (n=425) on Pap cytology were retrieved from the archives of 5 cytopathology laboratories. Availability of histology follow-up data and access to corresponding paraffin tissue blocks was a selection criterion. Cytology slides were stained for p16 using the CINtec Cytology Kit (mtm) and reviewed by two cytopathologists and cytotechnologists. The presence of cells immuno-reactive for p16 and showing morphologic abnormalities generated a positive test result. hc2 HR HPV testing (Qiagen) was performed on all specimens. Sections from the original tissue blocks comprising the lesions showing the worst morphology were prepared and used to establish an expert gynecopathologists consensus diagnosis that served as Gold standard for study purposes.
Results: For p16 cytology, sensitivity of adjudicated cytopathologist results for the identification of women with underlying CIN2+ reached 95% for ASC-US and 96% for LSIL cases. Specificity rates for p16 cytology slide reviews by the cytopathologists ranged from 66 to 71% for the ASC-US group, and from 47 to 53% for LSIL cases. For cytotechnologist reviews of the slides, sensitivity rates for CIN2+ were found at similar rates (ASC-US: 93%; LSIL: 92%), and specificity rates were 63% for ASC-US and 37% for LSIL cases, respectively. HPV testing resulted in sensitivity levels of 90% (ASC-US) and 96% (LSIL), and specificity rates of 38% (ASC-US) and 19% (LSIL).
Conclusions: Interpretation of p16 cytology slides has the potential to provide a comparable sensitivity, but significantly higher specificity for the identification of high-grade CIN as HPV testing in the triage of women with Pap cytology results categorized as ASC-US or LSIL.
Tuesday, March 10, 2009 1:15 PM
Platform Session: Section C, Tuesday Afternoon