Evaluation of the role of estrogen and progesterone in hormone replacement therapy (HRT) as a cause and promoter of breast cancer should begin with a study of the effect of these hormones on normal breast tissue. Cyclic alterations in the histologic changes of the breast in relation to menstruation have been confirmed in some studies. However, the histological influence on the breast of exogenous estrogen and progestin in postmenopausal women remains a very controversial subject, and there has been little consistency regarding the relative risk of HRT and breast cancer across many epidemiological studies. However, the Collaborative Group on Hormonal Factors in Breast Cancer has brought together and reanalysed about 90% of the worldwide epidemiological evidence on the relationship between breast cancer risk and the use of HRT. These analyses have revealed that the risk of breast cancer in HRT users is significantly increased. However, whether HRT affects mortality from breast cancer is not known.

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We investigated the number of readers for mammographic breast cancer screening using a questionnaire.
The questionnaire was distributed to members of the Japan Association of Breast Cancer Screening, the Japan Radiological Society, the Japanese Breast Cancer Society, the Japan Society of Obstetrics and Gynecology and the Japan Association of Obstetricians and Gynecologists, and 3, 925 replies were returned. Of these who replied, 1, 488 were obstetricians and gynecologists, 1, 292 were surgeons, 1, 014 were radiologists and 131 were others.
There were 2, 576 physicians who expressed an intention to read screening mammograms, but the number of well experienced physicians was only 882. The number of subjects screened is estimated to be about 2.4 million per year, and so 2, 000 physicians are needed in order to read the mammograms of 100 women per hour, and will be engaged in reading for 2 hours every month. There were sufficient physicians to read the screening mammograms, but those with an experienced eye were insufficient. A short course of mammogram reading is needed and expected for many physicians.

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At Hiroshima Atomic Bomb Casualty Council Health Management Center, mass screening for breast cancer among atomic bomb survivors (ATS) has been carried out since 1988 under the Atomic Bomb Survivors Medical Treatment Law. Furthermore, mass screening for women aged 30 years or older was started in 1989 under the Health Service Law for the Aged. Here we report the results of these screenings in Hiroshima city.
In the mass screening of ATS, examinees amounted to 22, 845, of whom 1, 051 required further examination. Of these, 990 actually underwent a further examination, and 62 patients with breast cancer were found, giving a detection rate of 0.27%. In contrast, a total of 76, 007 women participated in the mass screening for women aged 30 years or older, and further examination was required for 3, 748 examinees. Of these, 3, 406 actually received further screening, and 67 patients with breast cancer were found. The detection rate of breast cancer was 0.09%.
Since ATS are advancing in age, there are no longer any examinees in their fourth decade of life, and those in their seventh decade account for the largest proportion. The distribution of examinees by age is thus quite different between the two screening systems. When the detection rates of breast cancer as a function of age were compared between the two screening systems, the rate was higher in the mass screening for ATS. In terms of exposure status, the detection rate was highest among ATS who were within 2, 000 m from ground zero. Thus, mass screening for breast cancer might be useful for the health management of ATS.

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In our area, breast cancer screening has been carried out by both mobile screening and screening at our institute. The data for mobile screening over the four years between 1991 and 1994 was divided into a group screened mainly by physical examination (PE) and a group screened by physical examination and ultrasonography independently (PEU). The screening efficiencies of physical examination and ultrasonography were then studied. Besides these groups, data for screening at our institute were also examined as a reference group (REF). The detection rate of breast cancer was 0.04% in the PE, 0.22% in the PEU, and 0.10% in the REF groups. Among the breast cancers detected, cases that required further physical examination comprised 60% (3 of 5 detected breast cancers) in the PE, 37.5% (3 of 8) in the PEU, and 14.3% (2 of 14) in the REF groups. Therefore the screening efficiency of physical examination was not good. Cases that required further examination by ultrasonography comprised 100% (all eight) in the PEU and 85.7% (12 of 14) in the REF groups. Less than Tl breast cancers accounted for 40% (2 of 5) in the PE, 62.5% (5 of 8) in the PEU, and 92.9% (13 of 14) in the REF groups. Non-palpable breast cancers accounted for none in the PE, 37.5% (3 of 8) in the PEU, and 71.4% (10 of 14) in the REF groups.
In conclusion, the screening efficiency of ultrasonography was very good. It is thought that ultrasonography can frequently detect early breast cancer including non-palpable breast cancer, because it is carried out independently of physical examination by experienced ultrasonographers.

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The effectiveness of mammography screening has been proven in women aged 50 years or more ; however, this is not yet proven for women in their forties. We studied which modality was most effective for detection of breast cancer in different age groups. The subjects were 135 women with breast cancer who had been treated at Tsukuba University Hospital or Kinu Medical Association Hospital over the previous two years. All underwent three examinations : palpation (PALP), mammography (MMG), and breast ultrasound (US) at each hospital. Of the 135 patients, 53% were 50 years old or over, and 31.6% were in their forties. T1 breast cancer accounted for 53 of the 135 cases. When Tl breast cancer was the target of screening, all except one of the cancers in women aged 50 years or older were detectable by PALP and MMG combined, which is now being planned for mass screening. However, for those in their forties, this combination detected only 77.8% of T 1 breast cancers. The combination of PALP and US detected all cancers in women in their forties, and 96.9% in women aged 50 years or older. It is difficult to select the best screening modality from these results, because we were concerned only with detectability. Our results justify the combination of PALP and MMG for women aged 50 years or older ; however, the same method should not be applied to those in their forties. Flexible and meticulous consolidation is needed for women in their forties.

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Between 1994 and 1997, we detected 542 cases of breast carcinoma at our hospital. Of these, 43 cases (8%) with 60 foci were of the primary bilateral type, 17 (3%) with 34 foci were bilateral and simultaneous/concurrent, and 26 (5%) with 26 foci were bilateral and non-simultaneous/non-concurrent. For these bilateral types of breast carcinoma, we studied the advantages/usefulness of ultrasonography for revealing the clinical picture and providing detection opportunities. In bilateral and non-concurrent types of cancer, secondary cancer occurred gradually over an extended period of 20 years ; the longest interval was 43 years. A focal size of less than 1 cm in diameter was the most frequent, accounting for 23 cancer foci (38%). Nineteen foci (32%) were of the unpalpable type. The stages were classified as Tis 7 foci (12%), Stage I 33 foci (55%), and then early cancer was 58%. Ultrasonography (US) enabled us to detect all of our cases of bilateral breast carcinoma, while mammography (MMG) detected 55 foci (92%). Among 5 foci not detected by MMG, 4 were of the infiltrating cancer. Among breast cancer cases, contralateral incidence is said to be fairly high, and if malignancy is suspected in a unilateral breast, careful examination of the contralateral breast must be done and clinical follow up. Ultrasonography is effective/useful for the detection and diagnosis of breast carcinoma.

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Microcalcifications are one of the representative features of mammographically detectable breast cancers and are a very important symptom of early breast cancer. However, it is difficult to distinguish between benign and malignant microcalcifications. Therefore, we investigated the distinction between them on specimen radiograms of 22 benign and 15 malignant lesions.
So far we have considered shape, cluster, numbers, presence of a linear disposition, and irregularity of size and density when diagnosing microcalcifications, but judgement was difficult on the basis of these criteria. Therefore we revised these criteria and devised a new method of judgment. On the basis of the results, we made the following conclusions.
1) Shape of microcalcifications : If casting type calcifications are found inside clustered calcifications, we judge the case as malignant. Nearly half of all granular-type calcifications and pebble-like calcifications are malignant, and therefore judgement is difficult in these cases. We consider other types of calcifications to be benign.
2) Number of calcifications per 5 mm² and total number of calcifications : Even if we used these criteria, judgment was difficult.
3) Presence of a linear disposition : Probability of malignancy is high.
4) Irregularity of size and density : Even if we used these criteria, judgement was difficult. Statistical handling of means and standard deviations will be necessary in future.
5) The outline of the distribution and longest diameter/shortest diameter ratio : When the outline of the distribution becomes irregular and the ratio exceeds two, the probability of malignancy is high.
6) Developing density of parenchyma around clustered calcifications : The probability of malignancy is high.

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