LEAD TIME IN BREAST CANCER DETECTION AND IMPLICATIONS FOR PERIODICITY OF SCREENING1

Abstract

Shapiro S. (Health Services Research and Development Center. Johns Hopkins Medical Institutions. Baltimore. Md. 21205), J. D. Goldberg and G. B. Hutchison. Lead time in breast cancer detection and implications for periodicity of screening. Am J Epidemiol 100:367–366, 1974.—The Health Insurance Plan of Greater New York (HIP) randomized clinical trial of the value of repetitive screening for breast cancer with mammography and clinical examination has shown a one-third reduction in mortality from breast cancer over a 5-year period. This has generated interest in the periodicity of future breast cancer screening examinations. To deal with this issue, the experience in the HIP study was used to estimate the average lead time gained through screening in the detection of breast cancer among the women who were aged 40–64 years at the start of the screening program. The statistical models that were applied suggest that the average lead time is about a year; at the initial examination, the gain is estimated at 7 months; at subsequent screenings conducted about a year apart, the gain is estimated at 11–13 months. Additional years of follow-up after termination of screening are projected to determine how rapidly the clinical incidence rate among the women in the screening program reaches the level of the rate expected in the absence of screening. Other investigators are applying different models to estimate lead time. However, it is likely that the estimates will fall in the interval of 1 to 2 years; a range that should be useful, for practical purposes, in considering periodicity of breast cancer screening programs.