A comparison of breast cancers detected by mass screening and those found in out-patient clinics.

We evaluated the results of a mass screening study on breast cancer detection by physical examination alone conducted in Ishikawa Prefecture from 1978 to 1990. The number of cases of breast cancer detected by mass screening was then compared with that found in out-patient clinics during the same period. Breast cancer was detected in 88 of 152,969 women by mass screening, the detection rate being 0.06% for the total study: 0.08% at the initial screening and 0.04% at periodic screenings. Early stage breast cancer was more frequently detected during periodic screenings than at the initial screening or in out-patient clinics. Moreover, although the initial screenings may have identified patients with breast cancer at more advanced stages, the survival was not significantly different. The results of this series led us to conclude that mass screening by physical examination alone may have no impact on the mortality rate of breast cancer.