Reference Manual - IARC Screening Group

Pathophysiology of Cervical CancerKEY CONSIDERATIONS FOR LOW-RESOURCE SETTINGSThe natural history of cervical cancer suggests that screening shouldinitially focus on women at greatest risk for high-grade dysplasia—women in their 30s and 40s. Although cervical cancer most oftendevelops in women after age 40, high-grade dysplasia (CIN II or III)generally is detectable up to 10 years or more before cancer develops,with a peak dysplasia rate at about age 35. Although unscreened womenover 50 remain at relatively high risk of cervical cancer, women in thisgroup who have had one or more negative tests in their 30s or 40s, are atmuch lower risk (see Figure 1-2, page 1-2).Data from some countries suggest that age-specific rates for CIN, CISand cervical cancer have shifted downward by about 5 years due, in part,to increasing STD and HIV/AIDS rates. If true, screeningrecommendations in these countries may need to be adjusted accordingly.The observation of more cases in younger women, however, may just bea reflection of changes in the age structure of the population or ofcervical cancer screening patterns, rather than a shift in age-specific rates.ANATOMY AND PHYSIOLOGY OF THE NORMAL CERVIXAge-RelatedChanges in theTransformationZoneDuring the first 18 to 20 weeksof embryonic life, the originaltall (columnar) cells that line thevagina and cervix are graduallyreplaced by flat (squamous)cells. As shown in Figure 3-2,throughout early childhood anduntil puberty, the squamous cellsmeet the remaining columnarcells at the squamocolumnarjunction (SCJ), a thin line wellout on the face of the cervix. 2Figure 3-2. The Cervix at PubertyAdapted from: Rubin 1999. 22 Reprinted with permission from ADVANCE Newsmagazines.3-2 Cervical Cancer Prevention Guidelines for Low-Resource Settings