[Mass screening for breast cancer in Japan].

To establish effective mass screening projects for breast cancer, our study group (Tominaga group) was co-sponsored by the Ministry of Welfare. From 1968 to 1986, 643,513 women at the initial screening and 719,189 women at the subsequent screening were examined by physical examination. Abnormalities were found in 24,864 (3.9%) and 23,880 (3.3%) of these women, respectively. Cancer was detected in 833 women (detection rate 0.13%) and 428 women (0.06%), respectively. To establish the criteria for assessing the life-prolonging effect of mass screening for breast cancer, clinical stage and prognosis of breast cancer detected by mass screening were compared with those for matched patients in outpatients clinics. Early stages were significantly more common in the patients detected by mass screening. The 5-year survival rate was significantly higher in the patients detected by mass screening (91.7% vs. 85.6%; P less than 0.01), but the difference with the other group was not significant (80.5% vs. 78.1%). Women who had conducted breast self-examination (BSE) showed a higher survival rate than those who had not. We were not able to confirm the general belief that interval cancer is more aggressive in nature and shows a poorer prognosis than the cancer detected through periodic screening.