The FACT-GP5 as a global tolerability measure: responsiveness and robustness to missing assessments.

ABSTRACT

PURPOSE: The Functional Assessment of Cancer Therapy item (FACT-GP5) has the potential to provide an understanding of global treatment tolerability from the patient perspective. Longitudinal evaluations of the FACT-GP5 and challenges posed by data missing-not-at-random (MNAR) have not been explored. Robustness of the FACT-GP5 to missing data assumptions and the responsiveness of the FACT-GP5 to key side-effects are evaluated. METHODS: In a randomized, double-blind study (NCT00065325), postmenopausal women (n = 618) with hormone receptor-positive (HR+), advanced breast cancer received either fulvestrant or exemestane and completed FACT measures monthly for seven months. Cumulative link mixed models (CLMM) were fit to evaluate (1) the trajectory of the FACT-GP5 and (2) the responsiveness of the FACT-GP5 to CTCAE grade, Eastern Cooperative Oncology Group (ECOG) Performance Status scale, and key side-effects from the FACT. Sensitivity analyses of the missing-at-random (MAR) assumption were conducted. RESULTS: Odds of reporting worse side-effect bother increased over time. There were positive within-person relationships between level of side-effect bother (FACT-GP5) and severity of other FACT items, as well as ECOG performance status and Common Terminology Criteria for Adverse Events (CTCAE) grade. The number of missing FACT-GP5 assessments impacted the trajectory of the FACT-GP5 but did not impact the relationships between the FACT-GP5 and other items (except for nausea [FACT-GP2]). CONCLUSIONS: Results support the responsiveness of the FACT-GP5. Generally speaking, the responsiveness of the FACT-GP5 is robust to missing assessments. Missingness should be considered, however, when evaluating change over time of the FACT-GP5. TRIAL REGISTRATION NCT00065325. TRIAL REGISTRATION YEAR 2003.

Researchers have been exploring the use of a single question, FACT-GP5 ("I am bothered by side effects of treatment"), as a quick way to learn about drug tolerability from the patients' perspective. This study explores if this single question can capture changes in tolerability during treatment, and if the assessment is missed by patients, whether that impacts the interpretation of tolerability. In our study, we found that the FACT-GP5 can be used to understand how tolerability changes during treatment. Missing assessments of the FACT-GP5 are important to account for when interpreting results. The FACT-GP5 may be a useful question for capturing the patient experience of drug tolerability.