Strengths and limitations of the study
Strengths of this study include its international character, its randomised controlled design and the high rate of intervention group participants who completed the advance care planning programme. In addition, we were able to include core cost categories (hospital care, diagnostic procedures, medical interventions and medication) in our economic evaluation. Our study has some limitations as well. In some countries, more intervention than control patients were included while in others this was the other way around. We do not expect this hugely biased our estimates since the inclusion criteria were similar in all countries and we purposefully defined them objectively, using terms of the TNM classification and staging system. However, given that usual care may differ between countries, for instance more or less routine discussions about care preferences, this may have impacted the contrast between intervention and control group. Also, there is the possibility of professional gatekeeping and that patients who were already more oriented towards advance care planning more often agreed to take part in the ACTION study, as far as it concerns the intervention group. We hypothesise that participating in advance care planning may have been less appealing to patients who were focused at cure. Therefore those invited to participate in the intervention group may have more often declined than those invited to participate in the control group. Lower response rates in intervention hospitals may have resulted in a selection bias, since in the intervention group fewer patients than in the control group received systemic therapy (79.2 vs 88.9%, respectively) and fewer had WHO performance status 0 (fully active) than in the control group (24.9 vs 39.8%, see 