Screening for cancer: state of the art and prospects for the future.

Effectiveness of screening has been established for two cancer sites: breast and cervix uteri. Only for these, therefore, are national policies applicable. The degree of effectiveness of such programs will depend on the coverage of the eligible population; organized programs are, therefore, essential. For cancer of the cervix, nearly maximal efficacy will be obtained by screening sexually active women from 25 to 60 years of age every 3 years. For cancer of the breast, current evidence only justifies screening from 50 years of age; most programs will stop at 70 years of age. Mammography every 2 years will provide nearly maximal efficacy. The place of breast self-examination and physical examination of the breasts is under investigation. In Japan, screening for stomach cancer is justifiable, although strict evidence of effectiveness is lacking. Screening for other cancers must still be regarded as experimental, including the use of sigmoidoscopy and fecal occult blood tests for colorectal cancer, and visual examination of the mouth for oral cancer. Because of organizational and other difficulties, screening seems unlikely to make a major contribution to reduction in overall cancer mortality by the year 2000. However, if organizational problems can be overcome, screening has the potential to control invasive cancer of the cervix, and to make a major contribution to reduction in breast cancer mortality.