Defining Optimal Comorbidity Measures for Patients with Early Stage Non-small Cell Lung Cancer (NSCLC) Treated with Stereotactic Body Radiation Therapy (SBRT).

INTRODUCTION: Comparison of overall survival (OS) between SBRT and other treatments for early stage NSCLC is confounded by differences in age, performance status, and medical comorbidity. We sought to define the most robust measurement for this population amongst five indices: age, Eastern Cooperative Oncology Group (ECOG) performance status, Adult Comorbidity Evaluation-27 (ACE-27), Charlson Comorbidity Index (CCI), and age adjusted CCI (CCIa).

METHODS: 548 patients with stage I NSCLC treated with SBRT were analyzed. Patients were divided into "high" and "low" risk groups for OS for each index using the log-rank test. Continuous and dichotomized models were compared via Akaike Information Criterion (AIC) and the Vuong test. Multivariate Cox regression modelling was used with demographic information to determine the independent prognostic value of the continuous and dichotomized versions of the indices. The best was used to stratify the patients into as many significantly different cohorts as possible.

RESULTS: Optimal cut-points between "high-risk" and "low-risk" OS groups for age, ECOG, ACE-27, CCI, and CCIa were ≥75 years, ≥1, ≥3, ≥3, and ≥6 with HRs for death of 1.23 (95% CI: 1.00-1.50), 1.66 (1.28-2.15), 1.37 (1.12-1.67), 1.43 (1.17-1.76), and 1.47 (1.20-1.80) respectively. Dichotomizing did not result in a significant loss in prognostic power. While there was not a significant difference in prognostic power between the indices, CCIa best predicted OS. CCIa divided the patients into 3 cohorts with median OS of 42 months, 33 months, and 23 months for scores of ≤5, 6-7, and ≥8 respectively.

CONCLUSIONS: CCIa was the best indicator of OS in every model employed with no loss of prognostic power with dichotomization. Dichotomization of CCIa (≥6) could be implemented in future comparisons of SBRT with OS. No cohort could be identified with a median survival of less than a year where treatment could be deemed futile.