Validation of the Functional Assessment of Cancer Therapy - Immune Checkpoint Modulator 17-Item Symptom Index...

Immune checkpoint modulators (ICMs) have revolutionized cancer treatment but have unique immune-related adverse events (irAEs). The aim of this study was to develop and validate a brief measure of the most common, distressing, and diagnostically useful symptomatic irAEs.

Items were generated to assess symptomatic irAEs through a multistep process of (1) literature review and iterative expert input and (2) qualitative interviews of patients, caregivers, and clinicians regarding ICM-related irAEs and quality of life (QOL) impacts. An initial item set was administered across five longitudinal or cross-sectional studies. The final item set was selected using a Delphi method; validity, reliability, minimally important differences (MIDs), and sensitivity to change were evaluated.

Qualitative interviews with 14 patients, seven caregivers, and six clinicians informed an initial set of 46 symptomatic irAEs, which was administered to patients (N = 503, 52% female, mean age = 64) treated with ICMs for non-small cell lung cancer (n = 342), head and neck cancer (n = 72), renal cell carcinoma (n = 43), or melanoma (n = 46). A final item set was selected and mapped to FACIT library items. This produced the 17-item FACT-ICM Symptom Index, which showed reliability (α = 0.86), construct validity (comparative fit index = 0.93), convergent validity with validated measures of physical QOL (r = 0.69-0.73), discriminant validity with emotional and social QOL (r = 0.03-0.65), and criterion validity (i.e., better performance status was associated with fewer concerns). Response option anchors adequately captured MIDs and were sensitive to change.

This brief 17-item FACT-ICM Symptom Index demonstrates initial construct, convergent, and divergent validity, reliability, MID, and sensitivity to change and is ready for use in research and clinical care.