PURPOSE In the United States, lung cancer accounts for 14% of cancer diagnoses and 28% of cancer deaths annually. Because no cure exists for advanced lung cancer, the primary treatment goal is to prolong survival. OBJECTIVES The study aim was to determine whether individual preferences, characteristics, and treatment experiences affect the meaning of treatment success. MATERIALS AND METHODS A quantitative study using an observational, longitudinal cohort of patients with advanced stage non-small-cell lung cancer was conducted. Data sources included medical records and patient interviews. Data were analyzed using x2, Fisher's exact, and McNemar's tests, as well as logistic regressions. RESULTS At the first interview of 235 individuals, 12% considered survival alone as their definition of treatment success; others defined treatment success as survival plus other aspects, such as quality of life and reaching an important personal goal. As they moved through chemotherapy, 47% of the patients changed their definition of treatment success. Bivariate analysis showed that patients with lower incomes tended to be more likely to change their definition of treatment success compared with their counterparts with higher income (P =.0245). CONCLUSION By taking chemotherapy, patients expect to increase their odds of survival and want to maintain the quality of life and functionality. A patient's definition of treatment success is often changing as treatment continues, making it appropriate to ensure patient-provider communication throughout their clinical care. The study results are limited to patients with advanced non-small-cell lung cancer and drawn from a predominantly white patient population, mainly from the US Midwest.