Sex Differences in Lung Cancer Survival: Do Tumors Behave Differently in Elderly Women?

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Abstract
Purpose Women with lung cancer appear to have better survival. Whether this results from better response to treatment, different tumor biology, or a longer life expectancy is not well understood. This study sought to assess sex differences in the natural history of lung cancer after controlling for unrelated causes of death and type of treatment. Methods This study included 18,967 elderly patients with stage I and II non–small-cell lung cancer diagnosed between 1991 and 1999 from the Surveillance, Epidemiology, and End Results registry linked to Medicare records. Patients were grouped into three categories according to the treatment received: surgery, radiation or chemotherapy but no surgery, and untreated cases. We used stratified and multivariate analyses to evaluate sex differences in survival using three methods to control for competing risks: lung cancer–specific survival, overall survival adjusting for comorbidities, and relative survival. Sensitivity analysis was used to test whether potential differences in smoking could account for the observed association of sex with survival. Results Women in all treatment groups had better lung cancer–specific, overall, and relative survival than did men (P < .0001). Stratified and multivariate analyses showed that women had better survival than did men after controlling for confounders. Sensitivity analyses showed that potential sex differences in smoking did not explain our findings. Conclusion In this national, population-based sample, elderly women with early lung cancer had better risk-adjusted survival regardless of the type of treatment. That sex differences were observed among untreated patients suggests that lung cancer in women may have a different natural history.