Test Characteristics of Specific p16 Clones in the Detection of High-grade Squamous Intraepithelial Lesions (HSIL).

p16 immunohistochemistry is recommended by the CAP-ASCCP Lower Anogenital Squamous Terminology (LAST) Standardization Project for human papillomavirus associated Lesions as an adjunct to morphologic assessment in the diagnosis of high-grade squamous intraepithelial lesion. This study evaluates the performance of different p16 clones as compared with E6H4 (CINtec) in detecting high-grade squamous intraepithelial lesion. The 54 high-quality articles addressing the performance of p16 identified by work group 4 of the LAST Project were evaluated for: specific p16 clone, scoring method, number of cases, anatomic site, and histologic diagnoses. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for each clone. Two-proportion z tests (pooled) were used to evaluate significance. In total, 32 of the 54 studies met the inclusion criteria. The most commonly used clone was E6H4 (17 studies, 3507 cases) with smaller numbers (1-4) of studies evaluating the following: 16P04, JC8, 16P07, G175-405, K5334, K5336, and 7962. p16 clones 16P04 and JC8 performed better than E6H4 with 16P04 exhibiting statistically significant higher sensitivity (94% vs. 87% for E6H4), specificity (94% vs. 81%), and positive predictive value (96% vs. 69%) while JC8 exhibited higher specificity (91% vs. 81%) and positive predictive value (88% vs. 69%). 16P07 performed similarly to E6H4 and the other 4 clones did not perform as well as E6H4. p16 clones 16P04, JC8, and 16P07 clones perform as well or better than the widely used p16 clone E6H4 (CINtec). However, further studies are indicated to determine the reproducibility of these findings and the impact of interlaboratory variation on test performance.

Utility of p16 Immunohistochemistry in Evaluating Negative Cervical Biopsies Following High-risk Pap Test Results.

The Lower Anogenital Squamous Terminology (LAST) Standardization Project for human papilloma virus (HPV)-associated lesions specifically recommends the use of p16 immunohistochemistry (IHC) as an adjunct to morphologic assessment of cervical biopsies interpreted as negative or low-grade squamous intraepithelial lesion (LSIL) from patients with prior high-risk Pap test results (high-grade squamous intraepithelial lesion [HSIL], atypical squamous cells cannot exclude HSIL, atypical glandular cells [AGC], or HPV16 atypical squamous cells of undetermined significance [ASC-US]). The impetus for this recommendation is to increase detection of missed high-grade disease. However, the quality of evidence supporting this recommendation was lower than that for the other LAST recommendations addressing improved consistency in the diagnosis of HSIL with the use of p16. A database search spanning 10 years identified 341 cases (encompassing 736 discrete biopsy specimens) interpreted as negative for dysplasia from 330 patients with a prior high-risk Pap result (atypical squamous cells cannot exclude HSIL, HSIL, atypical glandular cells, not otherwise specified [AGC-NOS], atypical endocervical cells--NOS [AEC-NOS], and AEC-favor neoplastic). p16 IHC was performed and detected missed abnormalities in 11/341 (3.2%) cases. The abnormalities corresponded to missed foci of HSIL (cervical intraepithelial neoplasia [CIN] 2) (n=1), SIL-indeterminate grade (n=7), atypical squamous metaplasia (n=2), and LSIL [CIN1]) (n=1). Subsequent histologic follow-up identified HSIL or greater in 6/8 (75%) p16 cases versus 20/79 (25.3%) p16 cases (P=0.0079). p16 IHC performed on biopsies interpreted as negative from patients with prior high-risk Pap test results increased the detection rate of missed SIL. A p16 result also significantly increased the likelihood of HSIL on subsequent biopsy. Although further studies are required to determine what percentage of missed HSIL justifies the additional cost, improved detection of HSIL in high-risk patients may lead to fewer diagnostic procedures and fewer patients lost to follow-up.