Theory and principles of cancer screening

Additional difficulties encountered in the assessment of screening programs include selection bias and overdiagnosis.  Selection bias assumes that women who are at higher risk (see Box 1-2 for a definition of “risk”)  for breast cancer will be more likely to participate in screening trials and will be more compliant with the recommended guidelines for screening mammography. Since cancer screening may be more beneficial and cost-effective for high-risk populations than for the general population, a selection bias may result in overestimation of the value of implementing a screening program for the general population.

“Overdiagnosis”  is the result of labeling small lesions as cancer or precancer when in fact the lesions may never have progressed to a life-threatening disease if left undetected and untreated. In such cases, some of the “cures” following early detection may not be real. This issue will be revisited in the next sections.


Sharyl J. Nass, I. Craig Henderson, and Joyce C. Lashof
Committee on Technologies for the Early Detection of Breast Cancer

National Cancer Policy Board INSTITUTE OF MEDICINE and Division of Earth and Life Studies

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