Breast cancer screening by mammography in women aged under 50 years in Japan

Background: The effectiveness of mammographic screening in women aged over 50 years has been confirmed in the United States and Europe, brit its effec tiveness in women aged from 40 to 49 years remains controversial. The optim um age for effective screening of subjects for breast cancer by mammography in Japan was studied based on the results of mammographic screening. Metho d: The benefit of breast cancer screening in women was examined by stratify ing the results of mammographic screening in a Tokushima trial on the basis of age: under 50 years and 50 years or older The results of conventional s creening by physical examination alone, which we performed in a Zentsuji tr ial, were used as the control. Results: The examinees numbered 13,982 and 1 8,619 in mammographic screening and screening by physical examination, resp ectively. Breast cancer was detected in 43 and 22 patients, respectively. T he detection rate of breast cancer was 0.31% by mammographic screening, whi ch is about 3 times higher than that (0.12%) by screening using physical ex amination. Mammographic screening thus showed significantly higher sensitiv ity (93.5% vs 73.3%, p=0.015). The proportion of stage I cancer and the abs ence of nodal involvement were 67.4% and 79.1% by mammographic screening, c ompared with 31.8% and 59% by physical examination. Our results obtained wi th mammographic screening were equal; to or higher than the results obtaine d in the United States and Europe. The clinical stage of the breast cancers detected by mammographic screening in the subjects aged under 50 yeats was stage a (DCIS) in one case and stage I in 10 cases, while the group aged 5 0 years or older showed stage 0 in 11 cases and stage I in 19 cases. There were thr ee cases of false-negative; two false-negative cases were aged und er 50 year, while one case was aged 50 years or older. The detection rates of cancer in the group under 50 years and that of 50 years or more were 0.1 9% and 0.39% by mammographic screening and 0.09% and 0.15% by the physical examination. The sensitivities in the group under 50 years and that of 50 y ears or more were 84.6% and 97.0% by mammographic screening and 72.7% and 7 3.7% by physical examination, showing no significant difference. In the res ults of mammograms by Wolfe's classification with respect to the age groups , the proportion of DY (dense breast) pattern decreased significantly from 3.5% to 0.2% in women of 50 years or more and from 16.6% to 2.4% in those u nder 50 years when the values were compared between the period from 1992 to 1995 and the period from 1998 to 1999 respectively (p<0.0001). Conclusion: The above findings suggested the possible effectiveness of mammographic sc reening not only in women aged 50 years or more but also in those aged unde r 50 years, in Japan. Therefore, introduction of mammography should be cons idered at an early date, even for women aged from 40 to 49 years.