Estimated cervical cancer disease state incidence and transition rates.

Cervical cancer was modeled as a disease of four states: disease-free (DF), carcinoma in situ (CIS), occult invasive (OI), and clinically invasive (CI). This model allowed transitions from DF to CIS, CIS to DF, CIS to OI, OI to CI, and DF to OI. Cases transiting from DF to OI after less than a year in the CIS state were included in the last category, which was called rapid-onset invasive disease. With the data from the British Columbia Cervical Cancer Screening Program (1955 through 1971) the disease-state transition-rate parameters for this model were estimated by least squares, and the fitted model was found to be in good agreement with the data. The estimates for parameters of particular interest were: average annual transition rate from CIS to OI, 3.7% +/- 0.6%/year; average annual transition rate from OI to CI, 48% +/- 1%/year; average annual transition rate from DF to CIS (after 1963), 1.1 +/- 0.1/1,000 person-years/year (= incidence rate of CIS); and average annual transition rate from DF to OI, 7.4 +/- 2/100,000 person-years/year (= incidence rate of rapid-onset invasive disease). Each year between 1.7 and 9.7% of all new cervical cancers and about one-third of all new OI cases were estimated to be of the rapid-onset variety.