Testing the validity and responsiveness of a new cancer-specific health utility measure (FACT-8D) in relapsed/refractory mantle cell lymphoma, and comparison to EQ-5D-5L.

BACKGROUND

The FACT-8D is a new cancer-specific, preference-based measure (PBM) of health, derived from the Functional Assessment of Cancer Therapy - General (FACT-G) questionnaire. The FACT-8D's measurement properties have not been tested to date. We assessed it's validity and responsiveness in relapsed/refractory mantle cell lymphoma (RR MCL) and compared the results to the EQ-5D-5L.

METHODS

Blinded analysis of pooled data from a phase 3 clinical trial. FACT-8D baseline and follow-up data (weeks 4, 7, 16, 31) were scored using Australian preference weights, the first available value-set. Convergent validity was assessed by estimating baseline correlations with the FACT-Lym total score, Trial Outcome Index (TOI), FACT-Lym lymphoma-specific sub-scale (LymS), EQ-5D Visual Analog Scale (VAS), and haemoglobin (HgB). Relevant clinical variables were used to categorise patients to test known groups' validity and responsiveness was investigated using data from baseline (n = 250) and week 31 (n = 130). Results were compared with EQ-5D-5L, scored using the UK 3L crosswalk and the 5L England value-sets.

RESULTS

The FACT-8D showed good convergent validity and responsiveness; baseline Pearson correlation coefficients between FACT-8D Index scores and other PRO measures were moderate to very strong (range: 0.49 for the EQ-VAS to 0.79 for FACT TOI) and the size of the change in FACT-8D Index scores at week 31 differed significantly (p < 0.005) between patients categorised as improved, worsened or stable using the FACT-Lym total score, LymS, and HgB. However, when assessing known groups' validity, FACT-8D failed to discriminate between patients categorised by health status on four of the seven variables analysed. Overall, FACT-8D and EQ-5D-5L performed similarly, although EQ-5D-5L showed better known groups' validity.

CONCLUSIONS

This is the first investigation into the psychometric properties of the FACT-8D. In this RR MCL trial dataset, it showed good convergent validity and responsiveness, but poorer known groups' validity, and EQ-5D performed as well or better on the tests conducted. The FACT-8D may offer an alternative method to generate utilities for the cost-effectiveness analysis of cancer treatments but needs further testing in other types of cancer patients. Evaluation of utility gains may have been limited by high baseline performance status in this RR MCL trial sample.