Abstract
Tochigi Public Health Service Association has provided breast cancer screening using a combination of mammography (MMG) and ultrasonography (US) since 2000. Among the 115,444 women examined in the 7 years since then, 285 (0.25%) were found to have breast cancer. The proportion of cases requiring more thorough examination has increased year by year, and reached 11.6% in 2006. Although from the beginning reference was made to previous images for mammographic interpretation, a system for reference to echographic interpretation was started in 2007. Introduction of this US reference system reduced the re-examination rate in 2008 to 8.0% (MMG 4.2%, US 4.7%). The proportion of identified cases requiring complete examination and consultation with medical institutions was as low as 75%, which is an issue related to quality control. Cancer was confirmed by both MMG and US in 155 cases (55%), by MMG in 81 cases (28%), and by US in 49 cases (17%). Cases that were stage 0 and I by the TNM classification comprised 78%, while lymph node metastases were present in 18%. Diagnostic benefit among test parameters was investigated by reference to age and mammographic density. The detection rate in patients in their 60s or older was higher with MMG than with US, whereas no such difference was evident in patients in their 50s or younger. With regard to mammographic breast density, cases showing an entirely fatty density or scattered fibroglandular density-2 were found more frequently with MMG. Taken together, in cases in their 50s or younger and those classified as having patterns of heterogeneous density or scattered fibroglandular density-1, MMG and US work in a mutually complementary manner, and their combined use in examinations is recommended. Nine years have passed since the introduction of MMG for breast cancer screening. Further effort is necessary to formulate and validate an effective and efficient structure for cancer screening.
