Introduction: Non-small cell lung cancer (NSCLC) is increasingly regarded as a heterogeneous group of diseases defined by specific gene mutations. Previous studies reported inconsistent results regarding the influence of epidermal growth factor receptor (EGFR) mutations on overall survival. This study assesses the effect of EGFR mutation on overall survival, and how the effects of other survival predictors are modified by EGFR mutation status, in non-squamous NSCLC patients.
Methods: The study was based on a population-based cohort of 1534 non-squamous NSCLC patients who were registered in northern New Zealand between 1 February 2010 and 31 July 2017. Kaplan-Meier analyses and log-rank tests were performed to assess the overall survival among different patient groups. Cox regression survival analyses were used to explore the associations between clinico-pathological factors and overall survival in terms of EGFR mutation status. The factors included were age at diagnosis, sex, ethnicity, smoking status, performance status, metastasis status and site of tumour.
Results: In this cohort, 20.2% had an EGFR mutation. The median overall survival was 0.79 years and 2.81 years in EGFR mutation-negative and mutation-positive groups respectively (log-rank p<0.0001). Metastasis status showed large and significant effects on overall survival in both EGFR mutation-negative and mutation-positive groups (hazard ratio, HR=3.6 and 3.3, respectively). In subgroup analyses by mutation status and metastasis status, overall survival decreased with an increase in age and decrease in performance status, and was lower in current smokers in all subgroups. In specific groups, females had lower survival only if mutation-positive; Māori had lower survival compared to NZ Europeans only if the disease was metastatic; and tumour site had significant effects on overall survival only in patients without metastasis.
Conclusion: EGFR mutation status and metastasis are the main predictors for overall survival in non-squamous NSCLC patients in northern New Zealand. The effects of age, smoking status and performance status are similar in all subgroups, but the effects of sex, ethnicity and site of tumour vary depending on EGFR mutation and metastasis status.