A model-based analysis of the HIP project for breast cancer screening.

A computer simulation approach is used to test assumptions about sensitivity of mammography and physical examination, and about the duration of preclinical screen-detectable breast cancer. Values between 50% and 80% for the combined sensitivity of the 2 tests give a good explanation of the results of the HIP randomized trial of breast cancer screening. The mean duration of the preclinical stage can vary from 1.6 years for high sensitivity values to 2.7 years for low values. In comparison with previous analyses of the HIP data our estimate for the sensitivity is lower, and the mean duration of the preclinical stage is longer. This is a consequence of the use of a more detailed model in our analysis, allowing for a more complete use of the HIP data in testing model assumptions. Similar analyses of data from recent screening projects in The Netherlands resulted in compatible estimates for the duration of preclinical breast cancer.