Screening for cancer.

Screening has proved effective for only two cancer sites, the breast and the cervix uteri. Only for these, therefore, should screening be a part of routine clinical practice. The degree to which screening is effective depends on whether appropriate groups are screened. For cancer of the breast, current evidence justifies mammographic screening every two years only from the age of 50, continuing at least to the age of 70. The place of breast self-examination and physical examination of the breasts is under investigation, but these procedures should probably be used in all women after the age of 40. For cancer of the cervix, nearly maximal efficacy is obtained by screening sexually active women every three years from the age of 25 to 60. Older women who have not been screened regularly should be screened. Other screening techniques to detect cancers, such as the rectal examination, sigmoidoscopy, and fecal occult blood tests for colorectal cancer, are still experimental. Organizational and other difficulties will prevent screening programs from making a major contribution to reducing overall cancer mortality by the year 2000. If organizational problems can be overcome, however, screening may control invasive cancer of the cervix and make a major contribution in reducing breast cancer mortality in the future.