Context Increased 5-year survival for cancer patients is generally inferred
to mean that cancer treatment has improved and that fewer patients die of
cancer. Increased 5-year survival, however, may also reflect changes in dia
gnosis: finding more people with early-stage cancer, including some who wou
ld never have become symptomatic from their cancer.
Objective To determine the relationship over time between 5-year cancer sur
vival and 2 other measures of cancer burden, mortality and incidence.
Design and Setting Using population-based statistics reported by the Nation
al Cancer Institute Surveillance, Epidemiology, and End Results Program, we
calculated the change in 5-year survival from 1950 to 1995 for the 20 most
common solid tumor types. Using the tumor as the unit of analysis, we corr
elated changes in 5-year survival with changes in mortality and incidence.
Main outcome Measure The association between changes in 5-year survival and
changes in mortality and incidence measured using simple correlation coeff
icients (Pearson and Spearman).
Results From 1950 to 1995, there was an increase in 5-year survival for eac
h of the 20 tumor types. The absolute increase in 5-year survival ranged fr
om 3% (pancreatic cancer) to 50% (prostate cancer). During the same period,
mortality rates declined for 12 types of cancer and increased for the rema
ining 8 types. There was little correlation between the change in 5-year su
rvival for a specific tumor and the change in tumor-related mortality (Pear
son r=.00; Spearman r=-.07). On the other hand, the change in 5-year surviv
al was positively correlated with the change in the tumor incidence rate (P
earson r=+.49; Spearman r=+.37).
Conclusion Although 5-year survival is a valid measure for comparing cancer
therapies in a randomized trial, our analysis shows that changes in 5-year
survival over time bear little relationship to changes in cancer mortality
. Instead, they appear primarily related to changing patterns of diagnosis.