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.