A case control study on the effectiveness of breast cancer screening by clinical breast examination in Japan

A case-control study was conducted in Miyagi and Gunma prefectures, Japan, to evaluate the effectiveness of breast cancer screening by clinical breast examination (CBE) alone in reducing breast cancer mortality. Case subjects, who were female and had died of breast cancer, were collected from residential registry files and medical records. Control subjects matched in sex, age and residence were randomly selected from residential registry files. The screening histories during 5 years prior to the cases having been diagnosed as breast cancer were surveyed using the examinee files of the screening facilities. Finally, the data of 93 cases and 375 controls were analyzed. The odds ratio (OR) of breast cancer death for participating in screening at least once during 5 years was 0.93 (95% confidence interval (95% CI) 0.48-1.79). The cases were more symptomatic than the controls when screened. If the participants who had had symptoms in their breasts were classified as not screened, the OR decreased to 0.56 (95% CI 0.27-1.18). The case control study suggests that the current screening modality (CBE) lacks effectiveness (OR = 0.93), although it might be effective for an asymptomatic population (OR = 0.56). The number of cases was small, and a larger case-control study is desirable to define whether CBE is effective or not. However, it is necessary to consider the introduction of mammographic screening to reduce breast cancer mortality in Japan.