[Symptom clusters in cancer patients]

Cancer patients often experience multiple symptoms simultaneously. These symptoms can, either individually or jointly, exert significant impacts on patients' lives. Recently, the focus of symptom research has shifted from individual symptoms to symptom clusters. The purposes of the current paper are to review the studies on symptom clusters and to provide suggestions for clinical practice and research. The symptom cluster has been defined as two or more symptoms that are correlated. Research on symptom clusters can be classified into three types. The first type usually identifies, on the basis of researchers' experience or previous studies, a single symptom cluster containing three to four correlated symptoms. The second type focuses on using statistical methods to identify multiple symptom clusters. The third type uses statistical methods to classify patients in accordance with their symptom profiles. The sickness behaviors induced by pro-inflammatory cytokines found in animal studies have been reported to be similar to symptoms experienced by cancer patients. This finding suggests a common etiology for cancer symptom clusters. Studies have identified some patient factors that correlate with the severity of symptom clusters, and have reported that some symptom clusters may exert a negative effect on the patient. The literature suggests two approaches to managing symptom clusters: utilizing the phenomenon of symptom overlap or utilizing potentially common physiological mechanisms. This paper also discusses unresolved issues in symptom cluster research.