Introduction: In order to evaluate the costs and cost-effectiveness of clinical treatments there is a need to be able to clearly define both the treatments and their costs. In our recent experience of conducting systematic reviews of clinical and cost effectiveness for the National Institute of Health and Clinical Excellence (NICE) we were challenged in our endeavours to conduct cost-effectiveness analysis related to best supportive care in lung cancer. This review was conducted as a contribution to such analysis. Objective: To identify and discuss the clinical components of best supportive care (BSC) packages for patients in lung cancer trials and to determine to what extent the conduct of clinical and cost-effectiveness analyses (CEAs) are fully informed. Design: Systematic review of RCTs, systematic literature reviews (SRs) and economic evaluations (EEs) which compare chemotherapy versus BSC for adult patients in lung cancer trials. Results:26 RCTs, 13 SRs and 41 EEs met the review inclusion criteria. Less than 50% of relevant studies included formal definitions of BSC. None of the papers included in the review adequately described or outlined the BSC options available to patients, how BSC was delivered or by whom. Data described in the studies do not facilitate the generation of a clear definition of a patient pathway in relation to BSC or a clear list of components or costs of such care. Conclusions: Failure to clearly define BSC packages means that comparison of treatment outcomes within and across trials is problematic. Formal definitions of BSC with set parameters for the common complications of advancing disease, not just the physical symptoms, need to be established to inform the design of future RCTs and CEAs. From an ethical perspective, it would seem appropriate to provide patients with an adequate definition of the care they could expect to receive within the comparator arm of a cancer trial. Health care professionals involved in the conduct and reporting of cancer trials must aim to communicate the BSC package delivered to patients.