Establishing mild, moderate, and severe scores for cancer-related symptoms: how consistent and clinically meaningful are interference-based severity cut-points?

Methods are presented to separate 16 frequently occurring cancer symptoms measured on 10-point symptom severity rating scales into mild, moderate, and severe categories that are clinically interpretable and significant for use in oncology practice settings. At their initial intervention contact, 588 solid tumor cancer patients undergoing chemotherapy reported severity on a standard 11-point rating scale for 16 symptoms. All reporting a one or higher were asked to rate on an 11-point scale how much the symptom interfered with enjoyment of life, relationship with others, general daily activities, and emotions. Factor analysis revealed that these items tapped into the same dimension, and the items were summed to form an interference scale. Cut-points for mild, moderate, and severe categories of symptom severity were defined by comparing the differences in interference scores corresponding to each successive increases in severity for each symptom. The cut-points differed among symptoms. Pain, fatigue, weakness, cough, difficulty remembering, and depression had lower cut-points for each category compared to other symptoms. Cut-points for each symptom were not related to site or stage of cancer, age, or gender but were associated with a global depression measure. Cut-points were related to limitations in physical function, suggesting differences in the quality of patients' lives. The resulting cut-points summarize severity ratings into clinically significant and useful categories that clinicians can use to assess symptoms in their practices.