p16INK4a immunocytochemistry on cell blocks as an adjunct to cervical cytology: Potential reflex testing on specially prepared cell blocks from residual liquid-based cytology specimens

BACKGROUND p16 (INK4a) (p16) is a well-recognized surrogate molecular marker for human papilloma virus (HPV) related squamous dysplasia. Our hypothesis is that the invasive interventions and related morbidities could be avoided by objective stratification of positive cytologic interpretations by p16 immunostaining of cell block sections of cytology specimens. MATERIALS AND METHODS Nuclear immunoreactivity for p16 was evaluated in cell block sections in 133 adequate cases [20 negative for intraepithelial lesion or malignancy, 28 high-grade squamous intraepithelial lesion (HSIL), 50 low-grade squamous intraepithelial lesion (LSIL), 21 atypical squamous cells, cannot exclude HSIL (ASC-H), and 14 atypical squamous cells of undetermined significance (ASCUS)] and analyzed with cervical biopsy results. RESULTS (a) HSIL cytology (28): 21 (75%) were p16 positive (11 biopsies available - 92% were positive for cervical intraepithelial neoplasia (CIN) 1 and above) and 7 (25%) were p16 negative (3 biopsies available - all showed only HPV with small atypical parakeratotic cells). (b) LSIL cytology (50): 13 (26%) cases were p16 positive (12 biopsies available - all were CIN1 or above) and 37 (74%) were p16 negative (12 biopsies available - all negative for dysplasia. However, 9 (75%) of these biopsies showed HPV). (c) ASC-H cytology (21): 14 (67%) were p16 positive (6 biopsies available - 5 showed CIN 3/Carcinoma in situ/Ca and 1 showed CIN 1 with possibility of under-sampling. Cytomorphologic re-review favored HSIL) and 7 (33%) were p16 negative (5 biopsies available - 3 negative for dysplasia. Remaining 2 cases - 1 positive for CIN 3 and 1 showed CIN 1 with scant ASC-H cells on cytomorphologic re-review with possibility under-sampling in cytology specimen). (d) ASCUS cytology (14): All (100%) were p16 negative on cell block sections of cervical cytology specimen. HPV testing performed in last 6 months in 7 cases was positive in 3 (43%) cases. CONCLUSION p16 immunostaining on cell block sections of cervical cytology specimens showed distinct correlation patterns with biopsy results. Reflex p16 immunostaining of cell blocks based on the algorithmic approach to be evaluated by a multiinstitutional comprehensive prospective study is proposed.