Reference Manual - IARC Screening Group

THREEPATHOPHYSIOLOGY OF CERVICAL CANCERBACKGROUNDA clear understanding of the natural history of cervical cancer is key toplanning and implementing a rational, cost-effective cervical cancerprevention program. Accepted models of the natural history of cervicalcancer have changed in recent years. Because the natural history of thedisease has a direct impact on testing, treatment and followup strategies,programs should base their decisions on the most current models.When programs to prevent or control cervical cancer were first developed,it was assumed that cervical cancer developed from precancerous lesions(broadly known as dysplasia 1 ), progressing steadily from mild to moderateto severe dysplasia and then to early cancer (CIS) before invasive cancerdevelops. In fact, it now appears that the direct precursor to cervical canceris high-grade dysplasia (CIN II or III), which can progress to cervicalcancer over a period of up to 10 years or more (Figure 3-1). Most lowgradedysplasia (CIN I) disappears without treatment or does not progress,particularly those changes seen in younger women. Prevalent cases,however, where disease has been present for a longer period of time, areless likely to regress. This is the situation that exists when cervical cancertesting is first being started in a country or region.Figure 3-1. Natural History of Cervical Cancer—Current UnderstandingSource: PATH 1997.1 For definition of dysplasia, see the Glossary.Cervical Cancer Prevention Guidelines for Low-Resource Settings 3-1