Development of a breakthrough cancer pain assessment tool

Abstract

Breakthrough cancer pain (BTCP) is a type of pain characterised by transient pain exacerbations on the background of stable and well-controlled pain. It is a significant problem in cancer patients, however, there are no fully validated diagnostic or measurement instruments to identify and assess this type of pain. The aim of this study was to develop and validate a clinical tool to diagnose and quantify BTCP. This study consisted of two stages. Stage one involved the development of a BTCP diagnostic algorithm, which was tested for diagnostic accuracy in 135 cancer patients. The ‘gold-standard’ BTCP diagnostic test for comparison was a comprehensive clinical assessment with a cancer pain expert. The sensitivity of the diagnostic algorithm to detect ‘true cases’ of BTCP was 0.54 (i.e. 54% of expert diagnosed BTCP cases screened positively), specificity 0.78 (78% of non-BTCP patients screened negatively), positive predictive value 0.84 (84% of cases that screened positively had the condition of BTCP), and negative predictive value 0.60 (60% of those that screened negatively did not have the condition). Stage two involved the development of a BTCP measurement instrument from first principles according to international standards. This instrument was then tested on 100 BTCP patients to assess for measurement properties of validity, reliability, responsiveness and acceptability. Reliability testing confirmed that there was an acceptable degree of measurement error. Validity testing confirmed two underlying BTCP dimensions in the instrument. All items and summary scores correlated appropriately with external measures of BTCP. The instrument demonstrated responsiveness by correlating with the patient impression of change and clinical measures of change. In summary, this is the first measurement instrument with robust validity and reliability data for the clinical diagnosis and quantification of BTCP. The measurement instrument met all required standards to recommend its general use however, the diagnostic tool had a lower than expected ability to detect ‘true’ cases of BTCP. The clinical implications of this study mean that once BTCP has been identified the measurement tool could be used to quantify the severity of BTCP, and monitor BTCP experience over time.