Impact of mammographic screening on the size and the relative frequency of invasion in breast cancers seen in a community hospital from 1975-1988.

Abstract

At CPMC routine mammographic screening was introduced in late 1975. The total volume of breast cancers, other than outside consultations, seen in the department increased from 71 in 1975 to 164 by 1988, an increase of 230%. This expansion in volume was due largely to surgical removal of mammographically detected occult, in situ duct and relatively small invasive duct carcinomas. In 1974, prior to routine mammographic screening, in situ carcinomas represented only 4% of all breast cancers seen in the Department of Pathology at CPMC. However, after the introduction of mammographic screening, the proportion of in situ cancers increased steadily. By 1988, 45% of all breast cancers seen in our hospital were found by mammography. While data on the size distribution of invasive breast cancers are not available at our hospital prior to 1976, an appreciable effect of mammography is still evident when the numbers of relatively small invasive cancers detected in 1976 are compared with those detected in 1988. Invasive breast cancers 10 mm in diameter or less represented only 6% of all cancers in our series in 1976, but 33% in 1988. These findings confirm observations made by Gibbs on the pathology of breast cancers found in mammographically screened and unscreened populations. The detection of increasing numbers of relatively small invasive duct carcinomas produced an overall reduction in the average diameters of invasive cancers seen at CPMC. The average dropped from 30 mm in 1975 to a low of 14.8 mm in 1987. Mammography did not appear to be effective in the early detection of invasive lobular cancers and had no impact on reducing their size. The implications of early discovery of in situ duct and relatively small invasive duct carcinomas are for improved patient survival through: (1) preventing progression of in situ duct to invasive duct cancers, and (2) the removal of invasive duct cancers before reaching a size where there is a high risk of metastasis.