Early-detection programs have great intuitive appeal in oncology: Identifying a cancer in its infancy and "nipping it in the bud" appears a self-evident method for reducing morbidity and mortality. Petricoin and Liotta's logic, as described in the accompanying article, suggests that peptidomes should be effective in achieving this goal: "The earlier the cancer is detected," as made possible by proteomics, "the better the prognosis."1
However, we must not confuse early diagnosis with improved outcome. It has been observed that screen-detected cancers do tend, on average, to be earlier-stage malignancies, partly because more aggressive lesions are more likely to produce symptoms within a shorter period of time (Figure 1). Additionally, 5-year survival rates for stage I cancers are typically greater than for stage III or IV. This simply means the staging system works; survival rates are not equivalent to mortality rates. Five-year survival is the proportion of individuals alive five years ...
