# Validity, reliability, responsiveness, and clinically meaningful change threshold estimates of the National Comprehensive Cancer Network-Functional Assessment of Cancer Therapy-Breast Cancer Symptom Index (NFBSI-16)

## TL;DR

This study evaluates the psychometric properties of the NFBSI-16 tool for measuring breast cancer symptoms in patients with advanced disease.

## Contribution

The study provides new evidence on the validity and reliability of the NFBSI-16 and estimates meaningful change thresholds for clinical use.

## Key findings

- The NFBSI-16 shows acceptable internal consistency and validity for measuring breast cancer symptoms.
- Meaningful change thresholds were estimated for the DRS-P and Total scores using anchor-based methods.
- Responsiveness to worsening symptoms was demonstrated, but not to improvement due to limited data.

## Abstract

Breast cancer is one of the most common cancers in women. Patient-reported outcome measures are used to evaluate patients’ health-related quality of life in clinical breast cancer studies. This study evaluated the structure, validity, reliability, and responsiveness of the National Comprehensive Cancer Network-Functional Assessment of Cancer Therapy-Breast Cancer Symptom Index (NFBSI-16) subscales in a clinical trial featuring patients with advanced/metastatic breast cancer (aBC), and estimated NFBSI-16 meaningful change thresholds.

Data from 101 patients with aBC enrolled in a phase II trial (Xenera-1) were included for psychometric evaluation of the NFBSI-16. Subscale structure was evaluated by assessing inter-item correlations, item-total correlations, and internal consistency (cycles 2 and 5). Validity was assessed using scale-level convergent validity (cycles 2 and 5) and known-groups (Baseline). Reliability was analysed via test-retest at cycles 3–4, and responsiveness to improvement and worsening was evaluated at cycles 5, 7, and 9. Meaningful change thresholds were estimated using anchor-based methods (supported by distribution-based methods) at cycles 5, 7, and 9.

NFBSI-16 internal consistency was acceptable, but item-total correlations suggested that its subscales and the GP5 item (side-effect of treatment) scores may be preferred over a total score. Convergent and known-groups evidence supported NFBSI-16 validity. Test-retest reliability was good to excellent for Total and DRS-P (disease-related symptoms: physical) scales, and moderate for the GP5 item. Responsiveness to worsening was generally demonstrated, but responsiveness to improvement could not be demonstrated due to limited observed improvement. Anchor-based meaningful change thresholds were estimated for DRS-P and Total scores.

This study provides evidence that the NFBSI-16 has desirable psychometric properties for use in clinical studies in aBC. It also provides estimates of group- and individual-level meaningful change thresholds to facilitate score interpretation in future aBC research.

The online version contains supplementary material available at 10.1186/s41687-024-00776-y.