OBJECTIVES: To explore a) perception of bother, burden, and tolerability and b) clarity of the Functional Assessment of Cancer Therapy-General Item GP5 (FACT-GP5) questionnaire and association of FACT-GP5 response options with “high side-effect bother.”

METHODS: We conducted semi-structured 1:1 virtual qualitative interviews with consented on-treatment participants enrolled in LIBRETTO-531 trial (NCT04211337) who completed the FACT-GP5 at baseline. The FACT-GP5, a single-item measure, assesses the overall impact of treatment side-effects using a 5-point Likert scale (0=not at all to 4=very much) with a 7-day recall. Interviews consisted of a) concept elicitation regarding perception of bother, burden, and tolerability of treatment side-effects, and b) cognitive debriefing of the FACT-GP5 and the response options which were associated with “high side-effect bother”. Interview transcripts were thematically analyzed with inductive and deductive coding using ATLAS.ti. Saturation analysis was conducted to determine how much new information was obtained in each group of 5 interviews.

RESULTS: Interviewed participants (N=34) had a median age of 61 years (range=23–76) and 67.6% were male. Participants had a median time of 50 weeks (range=11–135) between the first day of study treatment and the interview date. Conceptual saturation related to bother, burden, and tolerability was achieved in the 4^th group interviewed. Concept elicitation indicated that side-effects were bothersome if they caused physical discomfort/annoyance, interfered with daily activities, and/or caused emotional distress. “Burden” implied a greater severity of side-effects or impacted daily activities more than “bother.” Most participants reported that bother and burden were related to their perceived “tolerability” of a treatment. Cognitive debriefing indicated that FACT-GP5 was clear, understandable, and relevant. Most participants (68%) indicated that options “3” or “4” were associated with stopping treatment and “high side-effect bother.”

CONCLUSIONS: The findings support the content validity of FACT-GP5 to assess treatment tolerability and the definition of “high side-effect bother” used in LIBRETTO-531.