Developing and testing a web-based intervention to encourage early help-seeking in people with symptoms associated with lung cancer.

The potential for differential dropout in online randomized trials requires careful consideration. Future help-seeking interventions should provide support for those who have previously felt dismissed by health professionals. The feasibility study provides some evidence that our 'TPB components' were effective, but validation in a powered trial is necessary. Statement of contribution What is already known on this subject? People with lung cancer often delay presenting symptoms to health services. Some patients (or their family/friends) look up symptoms online before their diagnosis, to decide whether they should see a doctor. Interventions are needed to ensure people can find useful information online that will encourage them to seek help for relevant symptoms. What does this study add? Theory-mapping and user involvement facilitated systematic intervention development. Lung cancer help-seeking interventions should address salient beliefs and personal relevance. The potential for differential dropout in online randomized trials requires careful consideration.