When should we stop screening?

Context: Although the age at which screening should be started is the subject of considerable debate, the question of when to stop has received little attention.

Count: Days of life lost by stopping screening at various ages.

Calculations: For each of three types of cancer (breast, cervical, and colon), we used life tables to calculate life expectancy at various ages for stopping screening and for continuing screening until death. The days of life lost by stopping screening is the difference in life expectancy between the two life tables for a specified age.

Data Sources: All-cause and cancer-specific mortality were obtained from the National Center for Health Statistics and Surveillance Epidemiology and End Results Survey (SEER). ASSUMPTIONS ABOUT BENEFIT: On the basis of randomized trial data, we used a 30% reduction in cancer-specific mortality for breast and colon cancer screening. Because there are no comparable data for cervical cancer, we assumed a 30% reduction in the mortality rate for the "best-guess" analysis and a 70% reduction in the mortality rate for the "best-case" analysis. We assumed that these benefits persisted for the elderly. ASSUMPTIONS ABOUT HARM: We assumed that there was no harm with screening.

Results: Given a starting age of 50 years, screening throughout life has a maximum potential life expectancy benefit of 43 days for breast cancer and 28 days for colon cancer. The average 75-year-old who stops either mammography or fecal occult blood testing would give up a maximum of 9 days. By stopping at age 80, she would give up a maximum of 5 days. Given a starting age of 20, Pap smear screening has a maximum potential benefit of 47 days in the best-case analysis and 7 days in the best-guess analysis. The average 75-year-old who forgoes Pap smear screening would give up a maximum of 3 days (best case) or 0.5 days (best guess). By stopping at age 80, she would give up a maximum of 1.5 days and 0.2 days, respectively.

Conclusions: Even assuming that the mortality reduction with screening persists in the elderly, 80% of the benefit is achieved before 75 years of age for breast cancer, 80 years for colon cancer, and 65 years for cervical cancer. The small benefit of screening in the elderly may be outweighed by the harms: anxiety, additional testing, and unnecessary treatment.