Background: Patient-reported outcome measures (PROMs) are commonly-used surrogates for clinical outcomes in cancer research. When researching severe diseases such as cancer, it is difficult to avoid the problem of incomplete questionnaires from drop-outs or missing data from patients who pass away during the observation period. The aim of this exploratory study was to explore patient characteristics and the patient-reported outcomes associated with the time-to-dropout.
Methods: In an Oncological Social Care Project (OSCAR) study, the condition of the participants was assessed four times within 12 months (t0: baseline, t1: 3 months, t2: 6 months, and t3: 12 months) by validated PROMs. We performed competing-risk regressions based on Fine and Gray's proportional sub-distribution hazards model for exploring factors associated with time-to-dropout. Death was considered a competing risk.
Results: Three hundred sixty-two participants were analyzed in the study. 193 (53.3%) completed a follow-up after 12 months, 67 (18.5%) patients dropped out, and 102 patients (28.2%) died during the study period. Poor subjective social support was related to a higher risk of drop-out (SHR = 2.10; 95%CI: 1.01-4.35). Lower values in health-related quality of life were related to drop-out and death. The sub-scales global health status/QoL, role functioning, physical functioning, and fatigue symptom in the EORTC QLQ-C30 were key characteristics of early drop-out.
Conclusion: Severely affected cancer patients with poor social support and poor quality of life seem more likely to drop out of studies than patients with higher levels of social support and a better quality of life. This should be considered when planning studies to assess advanced cancer patients. Methods of close continued monitoring should be actively used when patient experiences a substantial deterioration in their health-related quality of life and symptoms during the study. Results for such studies have to be interpreted with caution in light of specific drop-out mechanisms.
