The Fallacy of 5Year Survival in Indicating the Effectiveness of a Screening Program

The 5-year survival rate is frequently cited as evidence for the effectiveness of screening in reducing cancer mortality. Nearly every cancer has a longer 5-year survival for early-stage disease than late-stage disease. It should then follow that finding the cancer at an earlier stage leads to improved outcomes and lower mortality.

Factors other than the effectiveness of screening, however, are important determinants of the 5-year survival rate.15 As survival is defined as the time from diagnosis to death, it is heavily influenced by early detection, even if death is not postponed. Thus, improved 5-year survival for early-stage cancers could simply reflect the stage at which the cancer is found, with no effect of screening on the natural history of the cancer.

A second problem with the 5-year survival rate as a measure of the effectiveness of screening is related to the heterogeneity of cancers with the same name. Cancers diagnosed at an early stage may be pathologically different from cancers diagnosed at a later stage. Screening may have little to do with the higher 5-year survival rate for early-stage cancers: they would have lower malignant potential regardless of how (or when) they were detected.

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