Symptom clusters: the new frontier in symptom management research.

The majority of clinical studies on pain, fatigue, and depression associated with cancer are focused on one symptom. Although this approach has led to some advances in our understanding of a particular symptom, patients rarely present with a single symptom. Therefore, even though research focused on single symptoms needs to continue, it is imperative that symptom management research begins to focus on evaluating multiple symptoms, using cross-sectional and longitudinal study designs. In addition, research needs to focus on evaluating the relationships among multiple symptoms, specific interventions, and patient outcomes. One of the initial challenges in research regarding multiple symptoms is the terminology that should be used to describe the concept (e.g., symptom cluster, symptom constellation). Another significant area related to this aspect of symptom management research is determining the nature of clinically significant clusters of symptoms and their associated prevalence rates. Equally important is the need to determine what types of tools/instruments will provide the most valid and reliable data for the assessment of symptom clusters. Other areas that need to be considered as related to the assessment of symptom clusters include the establishment of cut points for symptom severity that would qualify a symptom for inclusion in a cluster; the focus of the assessment; and the choice of the outcome measures that will be used to judge the effect of a symptom cluster on the patient. In the area of intervention studies for symptom clusters, research will need to build on the limited number of clinical trials with single symptoms. Additional considerations related to research on symptom clusters include the determination of the mechanisms underlying the development of symptom clusters; the timing of the measurements for symptom clusters; and statistical challenges in the evaluation of symptom clusters. Research on symptom clusters in patients with cancer is cutting-edge science and a new frontier in symptom management research, and it needs to be done in tandem with research on single symptoms.