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 reside ntial registry files and medical records. Control subjects matched in sex, age and residence were randomly selected from residential registry files. T he screening histories during 5 years prior to the cases having been diagno sed as breast cancer were surveyed using the examinee files of the screenin g 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%Cl 0.27-1.18). The case contr ol study suggests that the current screening modality (CBE) lacks effective ness (OR=0.93), although it might be effective for an asymptomatic populati on (OR=0.56). The number of cases was small, and a larger case-control stud y is desirable to define whether CBE is effective or not, However, it is ne cessary to consider the introduction of mammographic screening to reduce br east cancer mortality in Japan.