LONG-TERM BREAST-CANCER SCREENING IN NIJMEGEN, THE NETHERLANDS - THE 9 ROUNDS FROM 1975-92

Study objective - To assess the performance of breast cancer screening in different age categories over two decades. Design - Important dete rminants of reduced breast cancer mortality such as attendance, mammog raphy performance, cancer detection, and disease stage were recorded. Setting - Nijmegen, The Netherlands, 1975-92. Subjects - Since 1975 mo re than 40000 women aged 35 years and older have been invited biennial ly for breast screening in a population based project in Nijmegen. Mai n results - Rates of attendance, referral, detection, and disease stag e were calculated, as well as the specificity of screening mammography and the predictive value of referral and biopsy. From round 3 onwards , the attendance rate of women younger than 50 years stabilised at 70% , in women of 50-69 years it was 62%, and in women aged 70 and over it was 22%. In these three age categories, the referral rates of a posit ive screening mammography per 1000 screened women were 4.9, 6.2, and 1 1.8, respectively. Specificity rates were between 99% and 100%. Curren t predictive values of referral were high: in the specific age categor ies 39%, 59%, and 68% of the referred women had cancer. Detection rate s remained fairly stable over the rounds 4-9, at 1.9, 3.6, and 8.0 can cers per 1000 screened women. In the two year period between screening the numbers of interval cancers per 1000 screened women were 2.2, 2.2 , and 2.9, for the three age categories respectively. With regard to i nvasive cancers detected during screening, the percentage of small tum ours (less than or equal to 20 mm on the mammogram) was 84% in each ag e category. For women younger than 50 years, the proportion of intradu ctal carcinoma in all the cancers detected at screening was 40%, while it was 15% in the other age categories. Conclusion - Throughout the n ine rounds, the screening outcomes were found to be adequate, particul arly considering the high specificity rate and the predictive value of referral without the interference of a low detection rate. Although t he occurrence of interval cancers seemed high, it was similar to other screening programmes. Despite a relatively low referral rate, the rat ios of screen detected versus interval cancer cases were favourable. W ell organised screening programmes can achieve good mammography result s without too many false positives. important that women participate i n a screening programme because cancer can still be detected even afte r several successive negative screening examinations.