Cdc6 has been extensively studied as a marker for cellular proliferation that is expressed during the normal cell cycle. Recent studies indicate that Cdc6 may be a marker for cervical intraepithelial neoplasia (CIN) and carcinoma; however, the histologic distribution of Cdc6 has not been explicitly defined. Expression of Cdc6 in the endocervical mucosa also remains unexplored.
The goal of the current study was to evaluate the distribution of Cdc6 protein, MIB-1 protein, and human papillomavirus (HPV) DNA in a broad range of cervical tissues, including normal, potentially premalignant, and malignant lesions of the ectocervical and endocervical mucosa.
We used an indirect immunoperoxidase method to stain formalin-fixed, paraffin-embedded tissues and frozen tissues, including biopsy and hysterectomy specimens, for Cdc6 and MIB-1 proteins, and we used in situ hybridization to detect HPV DNA in a subset of cases.
Cdc6 staining was exclusively nuclear and was present in both squamous and glandular epithelial cells of histologic sections. Cdc6 staining was rarely present in specimens of normal cervical squamous mucosa (2/84, 2.4%) or in specimens with squamous metaplasia (3/59, 5.1%) and was not detected in normal endocervical glands (0/84). Staining was present in most cases of CIN I (31/48, 65%). Staining was present in the majority of cases of CIN II (25/28, 89%) and in all cases of CIN III (36/36) and squamous cell carcinomas (34/34). The proportion of cells staining for Cdc6 increased with the grade of dysplasia, and the proportion of stained cells in squamous cell carcinomas was similar to that in lesions of high-grade dysplasia. Cdc6 staining was present in the majority of cases in glandular lesions including adenocarcinoma in situ (11/14, 79%) and adenocarcinoma (8/10, 80%). The histologic distribution of Cdc6-immunoreactive cells was similar to that of cells with a strong signal for HPV DNA, but Cdc6 protein and HPV DNA did not colocalize at the level of individual cells.
Cdc6 expression is a marker for high-grade cervical squamous and glandular dysplasia and carcinoma and is associated with HPV infection. The mechanistic basis of the association between HPV infection and Cdc6 immunopositivity remains to be determined but may represent either up-regulation of Cdc6 expression or stabilization of the Cdc6 protein.