AGE-SPECIFIC SENSITIVITIES OF MAMMOGRAPHIC SCREENING FOR BREAST-CANCER

The sensitivity of the mammographic screening test in the biennial scr eening program of Nijmegen is assessed by analyzing the occurrence of interval cancers, i.e, cancers surfacing clinically in the interval be tween a negative screening examination and the subsequent scheduled ex amination. The difference between the observed number of interval canc ers and the expected number of clinically manifest cancers in the abse nce of screening for the interval period reflects the number of cancer s detected by screening. The expected number should be limited by the number of those cancers that were not detectable at the time of the sc reening examination because their size was under the threshold of mamm ographic detectability (5 mm). In contrast to other sensitivity studie s we took these 'fast growing' cancers into consideration, the numbers of which are estimated in each of the six-month periods of the two-ye ar interval using age-specific tumor volume growth rates for three age groups: < 50, 50-69, and greater than or equal to 70 years. In patien ts under age 50, the sensitivity was 64% for cancers which would becom e clinically manifest within one year after screening. This sensitivit y was lower than those obtained from the 50-69 and greater than or equ al to 70 age groups, being 85% and 80%, respectively. For cancers that would become clinically manifest 12-18 months after screening, sensit ivity decreases to 22% in the under age 50 group, and to 56% and 65% i n the two above age 50 groups, respectively. We conclude that even whe n adjusted for growth rate, the mammographic screening test has a poor performance in the under age 50 group.