Evaluation of mass screening for thyroid cancer.

Mass screening for detecting both thyroid and breast cancer in adult women was carried out in Gunma Prefecture, Japan, between 1980 and 1986. The total number of subjects during the seven years was 152,651. The first screening was by inspection and palpation using experienced surgeons. Thyroid abnormalities were found in 5,902 subjects (3.9%) and 3,804 (2.5%) were required to attend a second examination. Thyroid carcinoma was detected in a total of 216 subjects, a detection rate of 0.14%. The detection rate for thyroid cancer was twice as high at the initial screening (0.19%) than that at subsequent periodic screenings (0.09%). Histological classifications of the detected thyroid cancers were: papillary carcinoma, 189 cases (87.5%); follicular carcinoma, 26 (12%); medullary carcinoma, 1 (0.5%). Eighty-seven percent of the thyroid cancers were asymptomatic at the time of screening. The tumor size were 2 cm or less in 126 patients (58.3%). Thyroid cancer detected by mass screening was revealed at an earlier stage and showed a significantly better survival rate compared to that of our usual outpatients. As differentiated carcinoma has been found at a higher incidence by mass screening, the program is useful for the early detection and treatment of thyroid cancer.