Abstract Background Understanding patient and health practitioner perspectives on clinical trials can inform opportunities to enhance trial conduct and design, and therefore patient experience. Patients with haematological cancers have faced additional risk and uncertainty during the pandemic but it is unclear how they and practitioners have experienced cancer trials during this period. In the context of a haemato-oncology trial (PETReA), we compared patient and practitioner views and experiences of PETReA before and during COVID-19. Methods Qualitative study embedded within PETReA. Semi-structured interviews (N=41) with patients and practitioners from 16 NHS sites before (n=17) and during the first wave of COVID-19 (n=24). Analysis drew on the framework approach. Results Practitioners acknowledged the need for the trial to continue during the pandemic but their treatment preferences altered, becoming more pronounced for patients who had a favourable response to induction treatment, while staying unchanged for patients with a less favourable response. Practitioners commented that COVID-19 meant the evidence base for the trial arms was lacking or mixed, but that it likely increased the risks of maintenance treatment for patients with a favourable response to induction treatment. While only one participant interviewed withdrew from PETReA during the pandemic, others said they would consider withdrawing if information that they were at increased risk of severe illness from COVID-19 became available. During COVID-19, patients described less frequent contact with the trial team, which left some feeling less clear about their trial pathway. However, several described having in-depth, collaborative discussions with practitioners about the risks and benefits of randomisation in the context of COVID-19. Patients valued these discussions and were reassured by the emphasis practitioners placed on patients being free to withdraw if circumstances changed, and this helped patients feel comfortable about continuing in PETReA. Conclusions The findings point to ways trial communication can support patients to feel comfortable about continuing in a trial during uncertain times, including adopting a more in-depth, collaborative exploration of the risks and benefits of trial arms with patients and emphasising voluntariness. The results are relevant to trialists recruiting patients who are clinically extremely vulnerable or are at increased risk of poor COVID-19 outcomes despite being vaccinated.