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 diagnosis:
finding more people with early-stage cancer, including some who would never
have become symptomatic from their cancer.
Objective
To determine the relationship over time between 5-year cancer survival
and 2 other measures of cancer burden, mortality and incidence.
Design and Setting
Using population-based statistics reported by the National 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 correlated 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 coefficients (Pearson and
Spearman).
Results
From 1950 to 1995, there was an increase in 5-year survival for each
of the 20 tumor types. The absolute increase in 5-year survival ranged from
3% (pancreatic cancer) to 50% (prostate cancer). During the same period, mortality
rates declined for 12 types of cancer and increased for the remaining 8 types.
There was little correlation between the change in 5-year survival for a specific
tumor and the change in tumor-related mortality (Pearson r=.00; Spearman r=−.07). On the other
hand, the change in 5-year survival was positively correlated with the change
in the tumor incidence rate (Pearson 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.