Cancer survivors who fully participate in the PROFILES registry have better health-related quality of life than those who drop out

Purpose Attrition and subsequent missing data pose a challenge in longitudinal research in oncology. This study examined factors associated with attrition in the PROFILES registry, and its impact on observed health-related quality of life (HRQOL) estimates. Methods Sociodemographic, clinical, and HRQOL data were collected annually from a cohort of 2625 colorectal cancer survivors between 2010 and 2015. Participant characteristics according to time of dropout were compared using analysis of variance and chi-square tests. Predictors of attrition were examined in logistic regression analysis. Multilevel linear mixed models were constructed to investigate associations between attrition and HRQOL over time. Results Participants who dropped out were more likely to be female (OR = 1.23, CI = 1.02-1.47), older (OR = 1.20, CI = 1.09-1.33), less educated (OR = 1.64, CI = 1.30-2.11), and to have depressive symptoms (OR = 1.84, CI = 1.39-2.44) than full responders, and less likely to have high socioeconomic status (OR = 0.74, CI = 0.61-0.94). Participants who dropped out earlier reported significantly worse HRQOL, functioning, and psychosocial symptoms, which declined at a steeper rate over time, than full responders. Conclusions Cancer survivors' HRQOL may be overestimated in longitudinal research due to attrition of the most unwell participants.