The use of p16INK4A immunocytochemistry in “Atypical squamous cells which cannot exclude HSIL” compared with “Atypical squamous cells of undetermined significance” in liquid-based cervical smears

Even though p16INK4a (p16) immunocytochemistry has proven a useful accessory tool verifying the identification of atypical squamous cells of undetermined significance (ASC-US) categorized smears, the procedure still has limitations. To date few studies examining the usefulness of p16 immunocytochemistry in atypical squamous cells which cannot exclude HSIL (ASC-H), compared with ASC-US in liquid-based cervical smears. Therefore, we examined the correlation of p16 immunocytochemical staining with follow-up biopsy results on ASC-H categorized smears and compared the data with those classified as ASC-US on 105 liquid-based cytology samples. We found no statistical significance in the p16 expression of ASC-US smears and the presence of squamous intraepithelial lesions (SIL) in follow-up biopsies (p = 0.546). However, p16 expression did significantly correlate with the presence of SIL (p = 0.002) in ASC-H smears. There was a statistically significant relationship between p16 expression and presence of high grade squamous intraepithelial lesions (HSIL) or more on the follow-up biopsies in both ASC-US (p = 0.012) and ASC-H (p < 0.001) categorized smears. In ASC-US categorized smears, there was no statistical significance between p16 expression and the HR-HPV viral load (p = 0.091). But there was a statistical significance between p16 expression and the HR-HPV viral load (p < 0.001) in ASC-H categorized smears. Our results indicate that p16 immunostaining is a much better useful marker for HR-HPV infection and detection of SIL in ASC-H categorized smears compared to those defined as ASC-US. Diagn. Cytopathol. 2010. © 2009 Wiley-Liss, Inc.