Abstract
Purpose
Patient-reported measures of overall side effect burden, such as the Functional Assessment of Cancer Therapy- item GP5 (GP5), can be used to inform the tolerability of cancer treatments and be included as an endpoint in clinical trials. The objectives of this qualitative study were to explore how participants with medullary thyroid cancer (MTC) conceptualize side effect bother, burden, and tolerability and to generate evidence to support the GP5 as a fit-for-purpose measure of patient-reported tolerability in the treatment of MTC and to establish which response options constitute “high side effect burden.”
Methods
A purposive sample of forty participants with MTC enrolled in the LIBRETTO-531 trial (NCT04211337) were recruited via clinical trial sites. Semi-structured interviews were conducted in the participant’s preferred language to examine the concept of tolerability, demonstrate understanding of the GP5 content, and establish which response options constitute “high side effect burden”. Interview transcripts were thematically analyzed with a mix of inductive and deductive coding methods.
Results
Concept elicitation results found side effect bother to be among the most proximal patient-reported concepts to tolerability and highly relevant to participants. The experience of side effects that are symptomatic and bothersome or burdensome are key contributors to how patients perceive the tolerability of a treatment. Cognitive interviewing showed the GP5 item was clear and understandable to all participants. Participants reported clear and concrete meaningful differences between each response option. Importantly, the qualitative data provide evidence that “high side effect burden” aligns with the response options of “Quite a bit” and “Very much” (score of 3 and 4, respectively) for most (60%, n = 24) interview participants.
Conclusion
Participants described the concepts of side effect bother, side effect burden, and tolerability as highly relevant and related. The GP5 assesses a concept important to individuals undergoing treatment for MTC in a way that is understandable and relevant. The definition of “high side effect burden” is appropriately reflected by scores of 3 or 4. This qualitative evidence is supportive of the GP5 as a fit-for-purpose measure of comparative tolerability in MTC.