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There is increasing interest in patient-reported measures of cancer treatment tolerability. A global measure of bother, the FACT GP5 item ("I am bothered by side effects of treatment") is potentially useful for regulatory, research, and clinical use. To understand this item's appropriateness for capturing treatment tolerability, we conducted cognitive interviews on this item with 3 samples of cancer patients.Patients with ovarian cancer (Study 1: N = 21; on treatment), lymphoma (Study 2: N = 14; on treatment), and colorectal or lung cancer (Study 3: N = 16; treatment naïve) were interviewed about GP5's understandability and relevance to their treatment side effects. What patients think about when answering GP5 was also assessed. In all studies, the interview included both structured and open-ended questions. Qualitative data were coded to extract themes and responses to structured questions were tallied.Most patients on treatment (Studies 1 and 2) reported that the GP5 item wording is appropriate (88%) and its meaning is clear (97%). They were very confident or confident in their response (97%) and stated that GP5 was relevant to their cancer experience (97%). When answering GP5, patients considered their treatment and specific side effects. A large proportion (40%) of the treatment-naïve (Study 3) patients reported that GP5 was not relevant to their cancer treatment, and the largest proportion responded to GP5 thinking of negative side effect expectancies.This study provides assurance that GP5 is a useful indicator of treatment tolerability, and is meaningful to people with cancer, especially once they have started treatment.

12094 Background: The Functional Assessment of Cancer Therapy patient-reported outcomes (PRO) item GP5 (“I am bothered by side effects of treatment”) estimates treatment tolerability. We aimed to extend our previous finding that GP5 predicts early aromatase inhibitor (AI) discontinuation (E1Z03, 96% White) in the racially diverse E1Z11 trial cohort. Methods: E1Z11 was coordinated by the ECOG-ACRIN NCI Community Oncology Research Program (NCORP) Research Base. Postmenopausal women initiating anastrozole per clinical care for ER+ stage I-III breast cancer with a pain score 0-3/10 and no rheumatologic comorbidities were eligible. Accrual of a racially diverse cohort of 1,000 women, including Black and Asian women, was planned. GP5 was administered prior to initiating anastrozole (trial baseline) and at 3, 6, 9 and 12 months. GP5 was scored on a 5-point Likert scale from 0 (not at all) to 4 (very much) and dichotomized as no/little treatment bother (0/1) or moderate/high treatment bother (2-4), consistent with previous analyses. A univariate Cox proportional hazards model estimated baseline GP5’s association with treatment duration via hazard ratio (HR). Early treatment discontinuation status was defined as treatment duration < 12 months with discontinuation not attributed to disease progression or death (n = 4), consistent with previous analyses. Results: 1,046 women enrolled from 6/2013-10/2018 (640 White, 201 Black, 205 Asian), including 590 (56%) from NCORP Community or Minority/Underserved Sites. Approximately 10% (100/987 with GP5 data) reported moderate/high treatment bother prior to initiating anastrozole. Anastrozole discontinuation rate at 1-year was 26.2% overall; it was lower among women with no/little treatment bother (25.7%, GP5 = 0-1) compared to moderate/high treatment bother prior to initiating anastrozole (34.7%, GP5 = 2-4; HR = 1.50, 95% confidence interval [CI]:1.04-2.15, p = 0.027). Subgroup analyses by racial cohort showed a similar predictive effect of GP5 in the White (n = 606, HR = 1.76, 95% CI: 1.12-2.77, p = 0.014) and Black (n = 184, HR = 1.85, 95% CI: 0.92-3.71, p = 0.079) cohorts, but not in the Asian cohort (n = 197, HR = 0.40, 95% CI: 0.10-1.62, p = 0.20). Conclusions: Moderate/high treatment bother prior to starting anastrozole was observed in 10% of patients and associated with a higher risk of early discontinuation, except in Asian patients. Our findings support the presence of a treatment tolerability threshold which can be compromised by pre-treatment burden. Treatment tolerability may also be influenced by cultural and genetic factors, which will be explored in further analysis of genetic and PRO data. Clinical trial information: NCT01824836.