Effectiveness of mammographic screening for breast cancer in women aged over 50 years in Japan.

The optimal age for effective screening of subjects for breast cancer by mammography in Japan was studied based on the results of two mammographic screening systems (systems I and II) in Tokushima Prefecture. System I consisted of visit screening using a bus equipped with a mammographic apparatus. System II consisted of central screening performed at Tokushima Health Screening Center. The examinees numbered 2,500 and 3,707 in systems I and II, respectively. There was a significant difference between the two screening systems in the age distribution of the examinees. The detection rates of breast cancer were 0.6% and 0.24% in systems I and II, respectively, which are 2-5 times higher than that (0.12%) obtained by conventional screening using physical examination alone. The detection rate increased especially in the sixth and seventh decades of life. The sensitivity of mammography screening was 93.3% in system I and 81.1% in system II. Higher sensitivity (100%) than that (73%) of screening by physical examination was obtained in women aged over 50. The proportion of stage I was 60% in system I and 66.7% in system II, compared with 32-65% in the United States and Europe. The rates of no nodal involvement were high, being 77.8% and 83.3% in systems I and II, respectively, compared with 57-71% in other countries. Breast-conserving therapy was applied to 18 of the 24 patients with breast cancer detected by the two screening systems. In addition, in Wolfe's classification of mammograms, the proportion of DY (mammary dysplasia) pattern was remarkably low, being 3.2% in the sixth decade and 0.8% in the seventh decade, compared with 16.6% in women aged 49 years. These results indicate that mammographic screening is effective in women aged over 50 years in Japan, as has been found in other countries.