We analyzed overall and disease-free survival (OS and DFS) after definitive (chemo)radiation for stage III non–small cell lung cancer with 2 statistical methods: Kaplan-Meier (KM) analysis, with diagnosis as index date, and conditional survival (CS) analysis, with a variety of disease-free index dates, and determined whether prognostic factors varied based on the reference date.
All 651 patients analyzed received definitive (chemo)radiotherapy for stage III non–small cell lung cancer in November 1998 to December 2010 at a single institution; all had Karnofsky performance status scores ≥60 and received ≥60 Gy. OS and DFS were first calculated with the KM method, and then CS was used to calculate 2 outcomes: OS conditioned on DFS time (OS|DFS) and DFS conditioned on DFS time (DFS|DFS). Factors predicting OS and DFS conditioned on 1-, 2-, and 3-year DFS were sought in univariate and multivariate analyses.
KM analysis produced 1-, 2-, and 3-year DFS rates of 48%, 30%, and 26%; OS rates were 64%, 41%, and 29%. By CS analysis, both OS|DFS and DFS|DFS showed an increase in 5-year OS after 6 months, and CS after 30 months approached 100%. On multivariate analyses, age and concurrent chemoradiation predicted OS|DFS; age, smoking history, tumor histology, disease stage, and radiation dose predicted DFS|DFS.
CS analysis showed that the probability of long-term survival increases sharply after 6 months with no evidence of disease; factors predicting survival differed based on the method and endpoint used.
*Departments of Radiation Oncology
†Thoracic/Head & Neck Medical Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX
Supported by Cancer Center Support (Core) Grant CA016672 to The University of Texas MD Anderson Cancer Center.
The authors declare no conflicts of interest.
Reprints: Daniel R. Gomez, MD, Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, At Unit 1150, 1840 Old Spanish Trail, Houston, TX 77054. E-mail: email@example.com.