Protein p16 as a marker of dysplastic and neoplastic alterations in cervical epithelial cells

Cervical carcinomas are second most frequent type of women cancer. Success in diagnostics of this disease is due to the use of Pap-test (cytological smear analysis). However Pap-test gives significant portion of both false-positive and false-negative conclusions. Amendments of the diagnostic procedure are desirable. Aetiological role of papillomaviruses in cervical cancer is established while the role of cellular gene alterations in the course of tumor progression is less clear. Several research groups including us have recently named the protein p16^INK4a as a possible diagnostic marker of cervical cancer. To evaluate whether the specificity of p16^INK4a expression in dysplastic and neoplastic cervical epithelium is sufficient for such application we undertook a broader immunochistochemical registration of this protein with a highly p16^INK4a-specific monoclonal antibody.

Paraffin-embedded samples of diagnostic biopsies and surgical materials were used. Control group included vaginal smears of healthy women and biopsy samples from patients with cervical ectopia. We examined 197 samples in total. Monoclonal antibody E6H4 (MTM Laboratories, Germany) was used.

In control samples we did not find any p16^INK4a-positive cells. Overexpression of p16^INK4a was detected in samples of cervical dysplasia (CINs) and carcinomas. The portion of p16^INK4a-positive samples increased in the row: CIN I – CIN II – CIN III – invasive carcinoma. For all stages the samples were found to be heterogeneous with respect to p16^INK4a-expression. Every third of CINs III and one invasive squamous cell carcinoma (out of 21 analyzed) were negative.

Overexpression of the protein p16^INK4a is typical for dysplastic and neoplastic epithelium of cervix uteri. However p16^INK4a-negative CINs and carcinomas do exist. All stages of CINs and carcinomas analyzed are heterogeneous with respect to p16^INK4a expression. So p16^INK4a-negativity is not a sufficient reason to exclude a patient from the high risk group. As far as normal cervical epithelium is p16^INK4a-negative and the ratio p16^INK4a-positive/ p16^INK4a-negative samples increases at the advanced stages application of immunohisto-/cytochemical test for p16^INK4a may be regarded as a supplementary test for early diagnostics of cervical cancer.