Does the Lightning Process Training Programme Reduce Chronic Fatigue in Adolescent and Young Adult Cancer Survivors? A Mixed-Methods Pilot Study Abstract Background: We report on a pilot intervention study exploring the efficacy of the Lightning Process® training programme for reducing chronic fatigue and improving health-related quality of life in cancer survivors. Methods: 13 adolescent and young adult cancer survivors previously treated for sarcoma or Hodgkin lymphoma were enrolled. A mixed-methods approach was applied. This involved the use of five validated patient-reported outcome measure (PROM) questionnaires at baseline and the three- and six-month follow-up points to obtain quantitative data. Semi-structured interviews were conducted after the intervention with emphasis on the participants’ experiences and outcomes. A reflexive thematic analysis was applied to the transcripts. Results: A significant reduction (p < 0.001) in the total fatigue score from baseline to the three- and six-month follow-up points was documented. The correlation coefficients between the various PROMs at baseline and the six-month follow-up point indicated considerable overlap between the measures. The qualitative findings of the interviews corresponded well with the PROM findings. Most participants experienced both less fatigue and explicit improvement in their energy level. The aspects of the intervention found to be particularly helpful were the theoretical rationale and the coping techniques mediated. Conclusion: These encouraging results here reported should be of interest to the general oncological community, although they require confirmation through a larger and controlled study.