Validation of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (QLQ-C30) as a measure of psychosocial function in breast cancer patients.

The European Organisation for Research and Treatment of Cancer (EORTC) quality of life questionnaire QLQ-C30 has been developed as a quantitative measure of health-related quality of life for use in clinical trials of cancer patients. Validity is an important measurement property of all scientific tests. This study contributes to the iterative process of validating the questionnaire by focusing on the psychosocial subscales of the QLQ-C30, using baseline data from 150 patients participating in a randomised trial of supportive group therapy for metastatic breast cancer. The results provide strong support for the discriminative validity of the global health/quality of life, role function and social function subscales of the QLQ-C30, in patients differing according to clinical criteria. The psychosocial focus of the trial enabled expansion of criteria used to form patient subgroups, beyond medical factors, and consequently support was demonstrated for the discriminative validity of the emotional and cognitive function subscales. The degree of support for these subscales was less substantial than for the other QLQ-C30 subscales as there were fewer relevant criteria. Convergence assessed by correlations with independent measures of psychosocial function provides strong support for the convergent validity of the emotional function, role function and global health/quality of life subscales of the QLQ-C30, and moderate support for the social function subscales. There was little opportunity for the cognitive function subscale to associate with conceptually analogous subscales. Further testing is recommended with more comprehensive and specific measures of cognitive status. In general, the psychosocial subscales of the QLQ-C30 appear to be measuring the concepts they are purported to measure.