A scoping review of breakthrough cancer pain: mapping the evidence landscape

Breakthrough pain (BTP) in cancer populations is characterized by heterogeneous definitions, assessment approaches, and management strategies. This scoping review mapped the available evidence to characterize BTP concepts, describe the evidence base, and identify knowledge gaps.

Following JBI methodology and PRISMA-ScR guidelines, we searched PubMed, Embase, Scopus, Cochrane Library, Web of Science, and Google Scholar for studies published January 1991-June 2025. Included studies employed quantitative designs investigating BTP definition, assessment, characteristics, or pharmacological management in adult cancer patients. BTP was defined conceptually as transient pain exacerbation occurring with controlled background pain; studies using varying operational criteria were included and categorized to examine definitional heterogeneity. Data were extracted by one reviewer using a piloted form and synthesized narratively with stratification by era, definition category, population, and intervention type. Consistent with scoping review standards, formal quality appraisal was not conducted; this review maps evidence without assessing strength or making recommendations.

146 studies (33 RCTs with 3,471 participants; 113 observational studies with 9,841 participants) were included. While 90% endorsed BTP as transient severe pain on controlled background pain, operational definitions varied substantially regarding pain intensity thresholds (range: no threshold to ≤ 4/10 background, ≥ 7/10 episode), opioid requirements (61% required regular opioids), and temporal criteria (12% specified duration limits). BTP characteristics showed marked heterogeneity: onset seconds to 30 min, duration 3-240 min, frequency 1 to > 10 episodes daily. Prevalence estimates ranged 33-95%, associated with definitional variation. Clinical trials predominantly evaluated transmucosal fentanyl using enriched enrollment (excluding 15-28% non-responders) and focused on pain intensity at 15-30 min. Industry sponsored 82% of trials. Evidence concentrated in resource-rich settings; minimal data from resource-limited regions.

This scoping review maps heterogeneous evidence characterized by inconsistent definitions, selected populations, short-term outcomes, and geographic concentration. Key knowledge gaps include: standardized operational definitions, patient-centered functional outcomes, long-term efficacy and safety data, evidence from diverse settings and populations, and integration of pharmacological and non-pharmacological approaches. The review provides a descriptive landscape but does not assess evidence quality or support treatment recommendations. Future guidance development requires expert consensus processes incorporating mapped evidence, clinical experience, resource availability, and patient values. Addressing identified gaps through rigorous, pragmatic research will strengthen the evidence base for BTP management.