For example, solar ultraviolet-B (UVB) and vitamin D were linked to cancer mortality in many studies [29-33]. Solar UVB doses are much higher in Honolulu than in LA. These unselected factors may explain the observed associations. To further eliminate this possibility, we performed a sensitive analysis to in- vestigate the association between air pollution and cancer survival in each city. As LA had over 95% of cases and higher air pollution level, we limited our ana- lysis in LA. The results from this analysis remain con- sistent. Therefore, the observed association between air pollution and respiratory cancer survival in this study is unlikely explained by potential confounding due to city- level factors.