P^16INK4A as an adjunct test in liquid-based cytology

OBJECTIVE: To assess the utility of P^16INK4A as an adjunct test in liquid-based cytology in cases with equivocal morphologic changes of high grade squamous intraepithelial lesion (HSIL). STUDY DESIGN: P^16INK4A immunoreactivity was investigated in residual ThinPrep material (Cytyc Corp., Boxborough, Massachusetts, U.S.A.) from 30 cases with equivocal diagnoses of HSIL that had corresponding follow-up biopsies. Two control ThinPrep cases were included: 1 HSIL with biopsy-confirmed cervical intraepithelial neoplasia (CIN) 3 and a negative specimen with a corresponding biopsy of squamous metaplasia. The expression of P^16INK4A in ThinPrep specimens and corresponding biopsies was scored as previously described. A ThinPrep case was scored positive if it contained > 10 abnormal cells with nuclear and cytoplasmic immunocytochemical staining. Corresponding biopsies were scored as having negative, sporadic, focal or diffuse staining. RESULTS: The p^16INK4A antibody assay was positive in 19 of 30 ThinPrep cases (63.3%). Seventeen of the 19 (89.4%) biopsies corresponding to the positively stained ThinPreps also were positive, with a score of at least focal positivity in the dysplastic regions (2 CIN 1, 4 CIN 2, 11 CIN 3; 2 lesions lost in the tissue recut). The assay was negative in 11 ThinPreps (36.6%) and 10 biopsies (33.3%) with tissue confirmation of chronic cervicitis (5), squamous metaplasia (2), CIN 1 (3) and 1 lesion lost in the tissue recut. Seventeen of 18 (94.4%) ThinPreps confirmed as high grade lesions upon biopsy showed P^16INK4A positivity. The control HSIL case with a CIN 3 biopsy was diffusely positive for P^16INK4A, and the control negative case with biopsy diagnosis of squamous metaplasia was negative. Nondysplastic squamous and metaplastic epithelium in 7 biopsies and nondysplastic squamous or metaplastic cells in ThinPrep cases were negative. Sporadic staining of bacteria, inflammatory cells and endocervical cells was noted. CONCLUSION: ThinPrep cases in the equivocal cytologic category with the corresponding tissue biopsy assayed for P^16INK4A expression showed that there was utility for this type of testing. A larger series comparing corresponding ThinPrep and tissue biopsies will be undertaken. The role of HPV infection in these cases will also be explored.