Incidence of latent breast cancer in Japanese women.

Detection of small or early neoplastic lesions is essential for the secondary prevention of cancer, and for this purpose information concerning their incidence and characteristics is required. Although data for latent or early cancers are available for various organs, details are limited in the case of the breast. The present investigation was carried out to cast light on the incidence of latent cancers, considered as lesions, in women with no symptoms and no palpable mass of the breast. Out of 2126 women visiting our hospital for initial breast examination during July to December in 1987, 542 (25.5%) had no complaint and neither a detectable mass on careful palpation nor a tumor shadow on mammography. However, 21 (3.9%) demonstrated microcalcification, 7 giving the impression of a possible malignancy. Subsequent biopsy of the 7 cases revealed 3 carcinomas. The detection rate of breast cancer in this population was thus 0.6% (3/542). Adopting the frequency (36%) of microcalcification detectable on mammography in 185 breast cancers diagnosed in this period as a base, the incidence of latent breast cancer among women visiting our hospital was calculated to be 1.5%.