PURPOSE: The aim of this study was to assess the difference in explained variance of Health-Related Quality of Life (HRQoL) between comorbidity, sociodemographic characteristics and cancer characteristics. This association was assessed among thyroid cancer, colorectal cancer, and (non-)Hodgkin's lymphoma patients.
METHODS: Data from three large population-based surveys on survivors of thyroid cancer, colorectal cancer, and (non-)Hodgkin's lymphoma were used. Cancer-specific HRQoL was assessed with the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire Core 30 (QLQ-C30) of which physical function, emotional function, fatigue, and pain were included in the analyses. Comorbidity was assessed using the Self-reported Comorbidity Questionnaire. The association between comorbidity and HRQoL was assessed with multivariate linear regression models. Semi-partial R (2) was reported to assess the amount of variance in HRQoL explained by comorbidity in comparison with sociodemographic and cancer characteristics.
RESULTS: In total, 3,792 cancer survivors were included in this analysis. The variance in HRQoL subscales explained by comorbidity was higher compared with sociodemographic and cancer characteristics for physical function (11-17 vs. 2-4 and 1-2 %, respectively) and emotional function (7-17 vs. 1-3 and 1-3 %, respectively), regardless of cancer type. In addition, comorbidity explained 7-20 and 11-13 % of the variance in pain and fatigue, respectively, compared to 0-4 % for both sociodemographic and cancer characteristics. Osteoarthritis and back pain were strongly associated with physical function and pain, while depression was strongly associated with emotional function. Depression and back pain were strongly associated with fatigue.
CONCLUSIONS: This study showed that comorbidity explained more variance in physical and emotional function, pain, and fatigue in comparison with sociodemographic and cancer characteristics in cancer survivors, regardless of cancer type. Our findings emphasize the importance of adjusting for the presence of comorbid diseases when assessing HRQoL in cancer survivors.
IMPLICATION FOR CANCER SURVIVORS: Cancer survivors suffering from comorbid diseases experience lower levels of health-related quality of life. Clinicians should become more aware of the impact of comorbidity on HRQoL and provide necessary psychological support to assist self-management of comorbid diseases.