The Utility of p16 Immunohistochemistry in the Diagnosis of Cervical Intraepithelial Neoplasia

Abstract

The morphologic diagnosis of squamous and glandular dysplasia in cervical biopsies may be complicated by a variety of inflammatory and hormonal conditions. Cellular changes associated with inflammation, pregnancy, and atrophy may mimic precancerous lesions. p16 Immunohistochemical staining has been shown to be one of a group of useful dysplasia markers in this setting. Five cases are presented to illustrate how p16 may be an aid in diagnosis. The advantages of p16 over other markers are also discussed. CASE REVIEWp16 has emerged as a useful biomarker for human papillomavirus (HPV) -related dysplastic and malignant lesions of the cervix. The p16 protein (also known as p16INK4A) is a cyclin-dependent kinase inhibitor that generally functions as a tumor suppressor and is inactivated in many cancers such as melanoma, glioma, leukemia, pancreatic carcinoma, and lung carcinoma. The protein has been found to be overexpressed in precancerous and malignant cervical lesions and is thought to be the result of inactivation of the retinoblastoma (Rb) protein by the E7 gene product of integrated HPV DNA. The Rb protein participates in a negative feedback loop with p16, whereby the inactivation of Rb leads to overexpression of p16. The expression of p16 has been extensively studied and it is widely accepted as a sensitive and specific marker of squamous and glandular dysplasia in the cervix. The use of p16 immunohistochemistry as a valuable adjunct in the diagnosis of difficult cervical biopsy specimens is illustrated in the following 5 cases. CASE REPORTS Case 1A 46-year-old patient was referred to colposcopy for an abnormal Papanicolaou (Pap) test and was found to have a cervical lesion confirmed on biopsy as cervical intraepithelial neoplasia (CIN) 3. A conization was performed and confirmed the presence of severe squamous dysplasia, CIN 3, involving the cervical epithelium from the 5 o'clock to the 6 o'clock position, with glandular involvement noted. Several deeper glands showed cellular and nuclear atypia characterized by nuclear stratification with nuclear hyperchromasia and mitotic activity. p16 Immunohistochemical staining of these glands showed a strong nuclear, as well as cytoplasmic, positivity, confirming their neoplastic nature and the diagnosis of high-grade endocervical gland dysplasia bordering on adenocarcinoma in situ (AIS) (Fig. 1). Case 2A 31-year-old had ASCUS (atypical squamous cells of undetermined significance) suggestive of LGSIL (low-grade intraepithelial lesion) on a Pap test and subsequently underwent cervical biopsy. The cervical biopsy specimen showed a rather intense infiltrate of acute and chronic inflammatory cells. The overlying epithelium appeared reactive, with enlarged nuclei displaying smooth nuclear contours and prominent nucleoli. There were areas of the epithelium, however, that appeared more disorganized with irregularly shaped and hyperchromatic nuclei, but still displaying prominent nucleoli. The differential diagnosis was between reactive changes and epithelial dysplasia. Immunohist...