A statistical model of the natural history of cervical neoplastic disease: The duration of carcinoma in situ

Abstract Estimates of the duration of the in situ stage of cervical intraepithelial neoplastic disease are presented in this report, based on the data obtained from Papanicolaou smear screening programs carried out in British Columbia, Canada, and Barbados, West Indies. Using established statistical techniques we have examined the properties of the expected age distribution of cases in a defined population at risk based on estimates of the age-specific incidence and prevalence rates of carcinoma in situ (CIS). We find that the duration of CIS in the aggregate is a variable that has a distribution with estimated upper and lower limits of the order of 10 and 3 years, respectively. Furthermore, based on these results we suggest that the natural history of the established CIS lesion is independent of the age of the woman at the time of incidence. The results presented here concerning the duration of CIS are contrasted with those reported by other workers. The differences in the estimates of the duration of CIS, or equivalently the transition time of this lesion in the aggregate, given here and those of other investigators are discussed. The application of the results presented in this report to the establishment of optimal intervals between Papanicolaou smear screening examinations is outlined.