Proliferation profile of benign and premalignant cervical epithelium as established by PCNA staining pattern

Proliferation in the normal cervix and in preinvasive cervical lesions

AIMS

To characterise further the proliferative compartment of the normal cervix and to document its alteration, if any, in the various grades of cervical intraepithelial neoplasia (CIN), particularly changes to the basal epithelial layer; to hypothesise as to the diagnostic and biological significance of any observed differences.

METHOD

Proliferative compartments from 86 cervical biopsy specimens (10 normal, 11 with koilocytic change only, 12 CIN I, nine CIN II, and 44 CIN III) were determined using microwave antigen retrieval and a standard three-step Streptavidin biotin peroxidase immunocytochemical technique incorporating the MIB-1 monoclonal antibody (directed against the Ki-67 antigen). Immunoreactivity was assessed as occupying either the lower one third, lower two thirds or all three thirds of the squamous epithelium. Basal cell positivity was also quantitated.

RESULTS

Specimens without CIN showed a thin suprabasal proliferative compartment two to four cells thick. True basal positivity was infrequent. With increasing grade of CIN, the growth compartment stretched evermore superficially so that in lesions of CIN III almost the full thickness of epithelium was cycling. In all grades of CIN, basal cell proliferation was significantly increased.

CONCLUSIONS

In normal cervix, the parabasal layers represent the main proliferative pool with the basal layer providing a reserve. When CIN supervenes, this proliferative compartment expands commensurate with the grade of dysplasia and as basal turnover is increased specifically the intimate relation between epithelium and basement membrane might be disturbed, facilitating invasion. The diagnostic utility of these changes in growth compartments is limited.

Semiautomatic PAPNET analysis of proliferating (MiB-1-positive) cells in cervical cytology and histology

With the event of microwave-antigen retrieval it has become possible to detect proliferating cells (staining positive for MiB-1) in cervical smears containing epithelial fragments and in paraffin sections containing cancerous cervical epithelium. The PAPNET system, using neural network computing, is able to collect from the slides epithelial fragments with positive-staining nuclei. The nuclei in epithelial fragments are semiautomatically quantitated using the PAPNET-digitized images. The parameter PPN (proportion-positive nuclei), in which the nuclear area of the positive nuclei is taken into account, prove to be superior to the proliferation index for distinguishing moderate dysplasia from carcinoma in situ. In repair cells, all four quantitative parameters are close to those of moderate dysplasias, indicating that this method is unfit for distinguishing these two entities. However, we show that MiB-1 staining is valuable for the analysis of "false-negative" and "false-positive" smears, and for quantifying proliferation in sections of carcinoma in situ.