Relative and combined performance of mammography and ultrasonography for breast cancer screening in the general population: a pilot study in Tochigi Prefecture, Japan.

BACKGROUND Breast cancer screening by mammography is thought to be effective in reducing breast cancer mortality while ultrasonography is not accepted as a population screening modality, although the latter has been suggested to be useful in detection of cancer in the dense breast, relatively more typical for a younger woman. METHODS Mammography with medio-lateral oblique view was offered on trial in 1999-2000 for 3453 female residents in Tochigi prefecture who also underwent clinical breast examination and ultrasonography. The municipalities that provided cancer screening were informed of the final diagnosis for women with positive findings in the screening trial by doctors who performed the diagnostic evaluation. Linkage was also made between the list of participants in the trial and registrations at Tochigi Cancer Registry for breast cancer cases diagnosed during 1999-2001. RESULTS Thirteen cases with breast cancer were identified during a 2-year follow-up period: 10 were diagnosed subsequent to positive finding in the trial; two were negative in the trial and diagnosed 23 and 24 months after, respectively; and one had a positive finding at the trial but was undiagnosed at first and then diagnosed 18 months after the trial. Among the 11 cases judged as positive in the trial, four were judged only by mammography while three were judged only by ultrasonography. Those mammography alone-detected cases were relatively young, at 36, 40, 47 and 54 years of age, respectively, while the ultrasonography alone-detected cases were aged 50, 55 and 68, respectively. CONCLUSIONS Combined screening with mammography and ultrasonography may be feasible. A larger study is required to evaluate relative performance of mammography and ultrasonography in detail by characteristics of examinees and their breasts.