The impact of comorbidity on Health-Related Quality of Life among cancer survivors: analyses of data from the PROFILES registry

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. 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 comorb 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 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. 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

Comparative performance of a modified landmark approach when no time of treatment data are available within oncological databases: exemplary cohort study among resected pancreatic cancer patients

Janick Weberpals,1 Lina Jansen,1 Geert Silversmit,2 Julie Verbeeck,2 Lydia van der Geest,3 Pauline AJ Vissers,3 Vesna Zadnik,4 Hermann Brenner1,5,6 1Division of Clinical Epidemiology and Aging Research, German Cancer Research Center (DKFZ), Heidelberg, Germany; 2Belgian Cancer Registry (BCR), Brussels, Belgium; 3Netherlands Comprehensive Cancer Organization (IKNL), Utrecht, The Netherlands; 4Epidemiology and Cancer Registry, Institute of Oncology Ljubljana, Ljubljana, Slovenia; 5Division of Preventive Oncology, National Center for Tumor Diseases (NCT) and German Cancer Research Center (DKFZ), Heidelberg, Germany; 6German Cancer Consortium (DKTK), German Cancer Research Center (DKFZ), Heidelberg, Germany Purpose: The Mantel–Byar method is the gold standard analytical approach to avoid immortal time bias, but requires information on the time between start of follow-up and exposure initiation. Alternatively, a modified landmark approach might be used to mitigate the amount of immortal time bias, which assumes exposure initiation at a predefined landmark time. In the context of an expected positive association between adjuvant chemotherapy (ACT) and overall survival among resected pancreatic cancer (PCa) patients, this study aims to empirically assess the performance of this approach relative to the Mantel–Byar method.Patients and methods: Data from resected PCa patients diagnosed between 2003 and 2014 and registered in the national cancer registries of Belgium, the Netherlands, and Slovenia were used to estimate the association between ACT and overall survival using a Cox proportional hazards model by country and overall. Results derived from the immortal time bias (misclassifying the time to ACT initiation), Mantel–Byar method, and conventional and modified landmark analyses with assumed cutoff times of ACT initiation at 9, 12 and 15 weeks post-diagnosis were compared.Results: In total, 5,668 patients with a total of 10,921 person-years of follow-up were eligible. All analytical approaches showed a significant survival benefit for resected PCa patients who received ACT, but immortal time bias analyses led to strong overestimation of ACT benefits compared to the Mantel–Byar method (immortal time bias: overall HR [95% CI] 0.68 [0.62–0.75] vs Mantel–Byar method: 0.82 [0.71–0.93]), whereas the conventional landmark approach generally provided rather conservative estimates (0.86 [0.75–1.00], 15 weeks landmark). HRs derived from modified landmark analyses depended on the cutoff time, but were similar compared to the Mantel–Byar method at 15 weeks (0.81 [0.70–0.94]).Conclusion: A modified landmark approach might be a valid alternative to the Mantel–Byar method if no time of treatment information is available. The performance depends on the chosen cutoff time. Keywords: immortal time bias, landmark analysis, pancreatic cancer, chemotherapy, population-base