Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
(continued)
aSmoking index is the number of cigarettes smoked per day × the number of cigarette-years.
Abbreviations: CI, confidence interval; HR, hazard ratio; MST, median survival time; OS, overall survival; PORT, postoperative radiotherapy.
