Premalignant Conditions of the Cervix

Elimination of reserve cells for prevention of HPV-associated cervical cancer

Human papilloma viruses (HPV), that are causative for most squamous cell cervical cancers (SCC), have a simple structure with only a few genes (six early and two late genes). Two of the early HPV genes (E6 and E7) are capable of transforming normal squamous epithelium into cancer. In the last 10 years, a controversial discussion arose as to which cells are primarily involved in cervical carcinogenesis. Virologists traditionally use a research model of stratified squamous epithelium, a permissive environment for completion of a full HPV-life cycle. Basic insights on HPV tropism, HPV life cycle, HPV-uptake, HPV-replication, HPV-gene expression were gained from this model. Stratified squamous epithelium, however, is a low-risk area for SCC. Most SCC develop in an area of endocervical columnar epithelium that undergoes squamous metaplasia. SCC arise after infection of immature squamous metaplasia, proliferating reserve cells/reserve cell hyperplasia and reserve cells of the endocervical columnar epithelium. Study models investigating this pathway of carcinogenesis do not exist and therapeutic consequences deduced from this knowledge are lacking. This review describes in detail cervical carcinogenesis after HPV infection of subcolumnar reserve cells and discusses new intervention strategies for patients. The WHO-launched global strategy to eliminate HPV-associated cervical cancer builds primarily on prophylactic vaccination, screening and treatment. New insights in cervical pathogenesis, may assist in reaching this ambitious WHO goal.

The origin of Human Papillomavirus (HPV) - induced cervical squamous cancer

Most research models of HPV-associated squamous cervical carcinogenesis focus on stratified glycogenated squamous epithelium, a permissive environment for HPV-life-cycle completion, while immature squamous metaplastic epithelium and reserve cells as targets of HPV-infection have received less attention. Subcolumnar reserve cells of urogenital sinus origin with a CK17/p63-phenotype serve as the primary stem cell for squamous metaplasia. The area of manifest or potential squamous metaplasia, referred to as transformation zone, is the site where most squamous cancers occur after a transforming HPV infection of proliferating reserve cells and/or metaplastic epithelium. Improper use of terminology, in particular confusion of transformation zone with transition zone (synonymous: squamous-columnar junction or SCJ), as well as poorly substantiated postulates of a stem cell niche at the squamous-columnar junction with 'embryonic stem cell markers' have complicated understanding of HPV-related squamous carcinogenesis. Reserve cells as target cells and reservoirs of HPV should move into future research focus.

CIN 3: the role of lesion size in invasion

OBJECTIVE

To define the relation between the size of a CIN 3 lesion (measured histologically) and invasive squamous carcinoma.

DESIGN

Measurement of CIN 3 by computerized planimetry of histological sections from 39 cone biopsies containing microinvasive cancer. Comparison with previous measurements of CIN lesions, associated with different grades of dyskaryosis.

RESULTS

Microinvasive carcinoma of the cervix is associated with extensive CIN 3 on the surface and in endocervical crypts. The mean size of CIN 3 lesions showing microinvasion is seven times greater than that for severe dyskaryosis without invasion, (P less than 0.0001) and a 100-fold greater than with mild dyskaryosis (P less than 0.00001).

CONCLUSION

Invasive squamous carcinoma of the cervix arises in large CIN 3 lesions and these are associated usually with severe dyskaryosis. We propose a model for the development of high-grade precancer as a small focus within low grade precancer which then undergoes expansion in size, accompanied by apparent progression in cytological grade.

Residual cervical intraepithelial neoplasia after laser ablation

Some patients with histologically proven residual cervical intraepithelial neoplasia after laser ablation have false negative cytology. The explanation for this is not known, but there was no evidence of buried lesions. Follow-up of all patients treated by selective ablation is necessary. Cytology alone is inadequate and careful, accurate pre- and posttherapy colposcopy is essential.

Stages in the evolution of squamous cell carcinoma of the uterine cervix: a critique of the concepts of "dysplasia" and "cancer"

A clinically detectable, frankly invasive, squamous cell carcinoma of the uterine cervix evolves through a series of step-like stages, at any one of which, except the last, its progress can be arrested. These stages are intraepithelial neoplasia, early stromal invasion, microcarcinoma and, eventually and irreversibly, invasive squamous cell carcinoma. Crucial to this concept of a series of plateaus in tumour development is the recognition that "dysplasia" is a differentiated intraepithelial neoplasm and the discarding of the term "cancer" in favour of the less emotionally loaded expression "neoplastic process".

Treatment of cervical intraepithelial neoplasia by colposcopically directed cryosurgery and subsequent pregnancy experience

Of 420 patients attending a colposcopy clinic 204 were treated with outpatient cryosurgery for cervical intraepithelial neoplasia. It was possible to assess a definite outcome of therapy in 159 patients, and the lesion was successfully eradicated in 87% of them. Treatment failure appeared to be more common in patients of high parity, when the lesion extended into the cervical canal, and in those patients with large lesions. Failure appeared to be unrelated to patient age and to the histological grade of the lesion. In subsequent pregnancies utero-cervical function was preserved.