different conclusions about who should be screened, how often, and by which tests (see Boxes 5.3 to 5.6).

Despite these inconsistencies, however, a core consensus has emerged about the appropriateness of certain types of cancer screening. There is essentially universal agreement across organizations that all adults age 50 and older should be screened for colorectal cancer, that all women should receive mammograms every 1 to 2 years beginning at least by age 50 (some say age 40), and that all sexually active women with a cervix should be screened regularly for cervical cancer. Of course, controversies about cancer screening persist, the details of which receive some attention in this report and are dissected in detail elsewhere (U.S. Preventive Services Task Force, 1996). The debate over whether men should routinely receive the PSA test symbolizes such controversies. A case study describing efforts to screen individuals for lung cancer, first using chest radiography and more recently using low-dose spiral computed tomography (CT), is presented in Chapter 7 to illustrate the dilemma of adoption of a new screening technology in the face of uncertain science.

From a public health perspective, the disturbing paradox is that the cancer screening tests for which there is a core consensus are not being administered to a large proportion of the Americans for whom they are recommended. Upward trends in the proportion of Americans receiving recommended cancer screening tests are heartening, but disparities in screening by socioeconomic status are substantial, many individuals are tested too late to obtain the full benefits of early detection, they are tested incorrectly, or their results receive inadequate follow-up. Chapter 6 examines the size of this gap and reviews evidence regarding potential strategies to improve the delivery of cancer screening services.