The pathology of cervical cancer

The preinvasive phase of squamous cell carcinoma of the cervix is a continuous spectrum of abnormal epithelium, which, for convenience of classification and as a guide to management, is customarily subdivided into three grades. The histological diagnosis of CIN, as well as the distinction between the grades, depends on a combination of features embracing aspects of differentiation, nuclear changes and mitotic activity. Grading of CIN is subjective. Generally, a minor degree of CIN would be expected to progress to a more severe form if not treated, but this progression does not seem to be inevitable; the more severe a CIN is at the time of diagnosis, the more likely it is that it will progress, both to a more severe degree of CIN and, eventually, to invasive carcinoma. Conversely, the more minor the degree of CIN at diagnosis, the more likely it is that it will regress. True figures are not available for the rate of progression from CIN to invasive carcinoma; it is sufficient to accept that the risk of progression probably occurs in a significant proportion of cases, if not the majority. Preclinical invasive carcinoma is divided into microinvasive carcinoma and occult invasive (Stage Ib) carcinoma. The definitions of these lesions have not yet been satisfactorily established; the term microinvasive carcinoma should define the maximum size of tumour which has virtually no metastatic potential and so may be treated in a conservative fashion. Invasive squamous cell carcinoma is classified histologically according to the cell type and the degree of differentiation, although it is debatable whether the cell type has any correlation with prognosis. Adenocarcinomas make up 5-10% of cervical cancers and a variety of histological types have been recognized. Adenocarcinoma in situ is being diagnosed with increasing frequency, often in association with squamous CIN. It seems apparent that AIS is a precursor of adenocarcinoma, but little is known about its natural history.