P16 Immunostaining Can Eliminate Approximately 20% Inaccurate Diagnosis of Low-Grade Squamous Intraepithelial Lesions (SIL) in Cervical Biopsies

Abstract

Introduction/Objective Differentiating low-grade SIL from reactive changes on light microscopy has remained controversial. P16 immunostaining is widely accepted in high-grade SIL unlike in low-grade SIL. We focused on the use of p16 immunostaining in eliminating inaccurate diagnosis of low-grade SIL on light microscopy. Methods A retrospective study on 60 cervical biopsies results over a 2 year-period was conducted using 35 suspicious cases for low-grade SIL (bi-nucleation and some nuclear atypia) and 25 low suspicion cases (enlarged nuclei but nuclear atypia cannot differentiate from reactive changes). All cases were stained for p16, significant nuclear expression of p16 was determined as low- grade SIL. Results After p16 immunostaining, 30/35 (85%) cervical biopsies from the suspicious group were found to be truly positive for low-grade SIL while 5/35 (15%) biopsies negative for p16 immunostaining were regarded as reactive changes. In the low suspicious group, 7/25 (28%) were found to be positive for low-grade SIL and 18/25 (72%) biopsies were negative, favoring reactive changes. The overall percentage of all 60 biopsies that showed a changed diagnosis based on p16 immunostaining was 20% (5 were truly negative in the suspicious group and 7 were truly positive in the low suspicious group). Using a 2 x 2 table with p16 as a gold standard for all biopsies, sensitivity and specificity of light microscopy for low-grade SIL were only 81% and 78% respectively. Conclusion Our study showed that p16 immunostaining can also be utilized to eliminate inaccurate diagnosis of low- grade SIL up to 20% in cervical biopsies.