Breast cancer screening: significance of minimal breast cancers

Analysis of cancers occurring during an aggressive screening program indicates: (1) In our study, during 3 years of active incidence screening of women under the age of 50 years, 24 cancers occurred, 14 of which were minimal. In the 3 years that there has been very limited screening, 23 cancers occurred, only five of which were minimal (p = 0.02393). (2) We projected that 110 breast cancers should have occurred in the incidence years of observation of this self-selected population of 10,531 women. In our screened population, 124 cancers occurred. This is not significantly different from the expected number. (3) In a similar period of observation of a similar sized screened population 112 cancers occurred in Louisville and 113 cases of cancer occurred in Seattle. There is no significant difference from the 124 cases reported in Cincinnati nor from the 110 cases expected. However, of all forms of cancer (prevalent, incident, interval) in Cincinnati, 67 cases were minimal, as against 35 in Louisville and 23 in Seattle (p = less than 0.0001). All in all, these data supported the concept that screening for breast cancer does not in any significant way increase the number of cancer cases detected, it only advances the stage of detection. The data also suggest that, for an aggressive screen, length-biased sampling does not seem to be an insurmountable obstacle.