[Current status and problems of breast cancer screening in Japan].

In cancer screening, it is essential to undertake effective screening with appropriate methodology. Effective screening should be supported by evidence of a reduced mortality rate. At present, mammography is the only method for breast cancer screening that has such evidence. However, mammography does not achieve sufficient screening accuracy in breasts with high mammary gland density. Dense breasts are common at ages below 50 and are more common in Japanese populations than in Western populations. As ultrasonography achieves better accuracy in breast cancer detection even in dense breasts, attempts to use it in screening have started. However, the specifications for ultrasound equipment and the procedures for examination and image reading have not been standardized, and the effectiveness has not been verified. The government therefore started the Japan Strategic Anti-cancer Randomized Trial (J-START) (http://www. j-start.org/), which is a controlled study to evaluate the effectiveness of ultrasound breast cancer screening conducted as a project in the Third-term Comprehensive Strategy for Cancer Control under the Basic Act for Anticancer Measures. This study makes a randomized comparison between 2 groups of women aged 40–49, 50,000 persons in each arm, who are screened using either combined screening with mammography and ultrasonography (intervention group) or mammography alone (control group), and evaluates the sensitivity and specificity as the primary endpoint and the accumulated incidence rate of advanced breast cancer as the secondary endpoint. J-START has been registered on the University Hospital Medical Information Network, ID: UMIN000000757. Although the outcome of cancer screening is reduction of the mortality rate, the planned study period (April 2006 to March 2011) is too short to confirm the results in this aspect, and we are investigating how to make evaluation possible in the future. This study is particularly important because breast cancer screening at ages 40–49 is challenging not only in Asia but also in Western countries.