[Objective] : The results of mass screening for breast cancer performed in Yokohama city were investigated by comparing the results of clinical breast examination (“mass screening group”) with those of breast cancer examination conducted in combination with mammography (“MMG screening group”). The accuracy and efficiency of the breast cancer examination were evaluated.
[Subjects and Methods] : The subjects were 192, 633 women over 30 years old living in Yokohama city who had undergone clinical breast examination during the 7 years from 1993 to 1999, and 3, 205 women mainly over 50 years old who had undergone clinical breast examination combined with screening mammography within the past 7 years (both groups included subjects who had undergone repeated examinations). Mammography was performed from two directions, and clinical breast examination was also conducted in combination to determine subjects who needed further examinations.
[Results] : Subjects who required further examinations numbered 14, 542 (7.5%) in the mass screening group and 838 (26.1%) in the MMG screening group. Breast cancer was found in 254 (0.13%) subjects in the mass screening group. In the MMG screening group, breast cancer was found in 27 (0.84%) subjects, among which 25 cases were detected by mammography and 4 were diagnosed as non-palpable breast cancer. Breast cancers not detected by mammography included one case of noninvasive ductal carcinoma manifested by thelorrhagia and one case of scirrhous carcinoma where the mammogram showed a dense breast.
[Discussion] : However, the ratio of subjects who were considered to require further examination was higher in the MMG screening group than in the mass screening group, and non-palpable breast cancers accounted for 14.8% of the cancers detected in the MMG screening group. These results suggest that screening mammography may contribute to the detection of early breast cancer.

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A study was conducted to evaluate the efficacy of a computer-aided detection (CAD) system for screening mammography (MMG).
Screening mammograms of 2, 231 women aged over 50 yr were examined. MLO images were obtained, and two expert observers interpreted the mammograms by consensus. First, each mammogram was interpreted without the assistance of CAD, followed immediately by a re-evaluation of areas marked by the CAD system. Data were recorded to measure the effect of CAD on the recall rate, cancer detection rate and detection rate of masses, microcalcifications and other findings.
The CAD system increased the recall rate from 2.3% to 2.6%. Six recalled cases were diagnosed as breast cancer pathologically, and CAD detected all of these lesions. Seven additional cases in which CAD detected abnormal findings had no malignancy. The detection rate of CAD for microcalcifications was high (95.0%). However, the detection rate for mass lesions and other findings was low (29.2% and 25.0% respectively). The false positivity rate was 0.13/film for microcalcifications, and 0.25/film for mass lesions.
The efficacy of the CAD system for detecting microcalcifications on screening mammograms was confirmed. However, the low detection rate of mass lesions and relatively high rate of false positivity need to be further improved.

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In 2000, biennial mammographic screening with physical examination was started for women aged over 50 yr in Japan. In this study we attempted to predict the future reduction of breast cancer mortality due to this screening program once it has become widely disseminated throughout the country.
The method used is a mathematical simulation model developed by the authors. Various numerical values are employed in the model, such as screening sensitivity, and mortality rate of screening-detected patients and that of outpatients. These values are obtained from the breast cancer screening research group organized by the Ministry of Health and Welfare.
It was found that for a 100% screening rate, the reduction in the relative risk of mortality (RR) is 0.60 to 0.69, which is a considerable reduction. However, for screening rates of 10% and 30%, RR is 0.97 and 0.90, respectively. These results clearly indicate that the screening rate is one of the most important factors affecting the success of cancer screening. We should aim at a screening rate of more than 80%, which has already been achieved in the EU countries.

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We compared the detection rate of breast cancer by mammography (MMG) or ultrasonography (US) screening in 39 women aged between 40 and 49 yr. The detection rates by MMG and US were 74.4% and 92.3%, respectively. For 26 asymptomatic patients without a palpable mass, the detection rates were 69.2% and 88.5%, respectively. The 39 cases were divided into 28 early-stage (stage 0 and I) and 11 later-stage (stage II and III) lesions. The MMG and US detection rates for early-stage lesions were 71.4% and 92.9%, and those for later-stage lesions were 81.8% and 90.9%, respectively.
These results indicate that US is more efficient than MMG for breast cancer screening in women aged between 40 and 49 yr.

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We investigated the current status of screening mammography in Oita and then examined the relationship between mammary gland dose and image quality using a RMI 156 phantom. There was a marked difference of mammary gland dose by a factor of 4.25 among facilities. This difference in dose may be due to differences in the mammography detection system and ages of the women examined. For the film-screen detection system, the image quality increased with increasing dose, whereas this was not the case for the CR system. Our findings suggest that screening mammography should be done using a highly sensitive film-screen detection system and a grid after determining the most suitable tube voltage for each facility.

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In 59 cases of breast cancer without palpable tumors in which nipple discharge was the main symptom (9.1% of all breast cancer cases), nipple discharge cytology, ductography, mammary ductoscopy, intraductal breast biopsy (IDBB) and cytology were evaluated for their cancer detection usefulness.
The cancer detection rate for discharge cytology at the first visit was 27.1% for the touch method and 28.6% for the collection method in which discharge was collected three times a day for three days. These figures were increased to 33.9% and 39.3% respectively by follow-up. Ductography revealed abnormality in 85.5% of cases, and intraductal lesions were observed by ductoscopy in 72.7%. IDBB under ductoscopic observation was performed in 18 cases, and carcinoma was diagnosed in 7 (38.9%). The cancer detection rate involving suspicious carcinoma was 66.7%. These results suggest a difficulty with pathology at the proximal portion of ductal carcinoma and the need for follow-up for early detection of intraductal carcinoma.

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