Cancer symptom clusters: old concept but new data.

Individuals with cancer have multiple symptoms, which frequently co-occur. A nonrandom distribution of symptoms suggests a common mechanism. Symptom clusters (SCs) were considered part of various syndromes in the early years of medicine. The SC concept in clinical medicine is old. Symptom clusters were commonly described in the psychology/psychiatry and neurology literature. Symptom cluster may be defined either clinically or statistically. Statistically derived clusters can differ from clinically defined clusters. The clinical importance of statistically derived clusters is unclear. Pain-insomnia-fatigue and pain-depression-fatigue are commonly recognized clinical clusters. Nausea-vomiting and anxiety-depression are also statistically observed clusters. The longitudinal stability of clusters is unknown. Certain SCs, appear to have a greater adverse influence on outcomes (such as performance status and survival) than others. Comorbidities probably influence symptoms at different levels, but their effect on cancer clusters is unknown. Comprehensive symptom assessment is crucial to cluster identification. The potential use of the cluster concept to abbreviate symptom assessment tools needs validation. Symptom cluster can be disease and/or treatment related and may change as individuals undergo antitumor therapies. Polypharmacy in symptom management is frequent but could be minimized if 1 drug could be used to treat cluster symptoms. Symptom cluster appears to vary with the assessment tool, disease stage, symptom domain used to cluster, cluster methodology, and number of symptoms assessed. The validity and reliability of SCs need universally accepted statistical methods, assessment tools, and symptom domains. For now, nausea-vomiting is recognized as a consistent cluster across multiple studies. Pain-depression-fatigue and pain-insomnia-fatigue are also well recognized. Symptom clusters may help in cancer diagnosis, symptom management, and prognostication. However, the cluster method, reliability, and validity need to be established before assessment or treatment guidelines are established. Symptom clusters require further research before becoming part of routine medical symptom assessment and management.