Trial of early detection of breast cancer by mass screening.

Since 1977, mass screening for breast cancer has been conducted in Miyagi Prefecture, Japan. The main activities consist of itinerant screening in the communities and group screening at the workplace. In addition, examinations were also carried out at a detection center. The total number of subjects examined was 90,076 in mass screening, with 4172 (4.6%) of them requiring a second examination. The overall breast cancer detection rate was 0.12% in the mass screening. In contrast, it was 3.1% at the center examination. Cytologic studies of nipple discharge were performed on 31,833 subjects. Positive findings were seen in 4 (0.004%). The incidence of smaller tumors was higher and that of nodal metastasis was lower in subsequent examinations than in the initial screening. In the high-risk group, who also underwent mammography at first screening, the detection rate was higher than that among general subjects examined.