Selection bias in follow-up studies of stem cell transplantation survivors: an experience within the Maastricht Observational study of late effects after Stem cell trAnsplantation (MOSA)

Hematopoietic stem cell transplantation is an important treatment for many malignant hematological and non-hematological diseases. Survivors of hematopoietic stem cell transplantation (HCT) are at risk of long-term health problems and reduced quality of life related to previous treatments. Many studies about these long-term effects have been conducted over the last decades. However, selection bias is a concern in long-term follow-up studies and little is known about the non-participating group. As part of the Maastricht Observational study of late effects after Stem cell trAnsplantation (MOSA), investigating long-term health effects by extensively phenotyping HCT survivors, we conducted a survey to characterise the non-participating group. This survey mostly focused on quality of life and physical complaints. The survey responders were generally older than the MOSA group, had more history of relapsed disease, and described their general health as bad or mediocre significantly more often than the MOSA group. Also, more deaths occurred in the group of non-participants between the start of study inclusion in 2015 and analysis of the survey results in 2021. This study suggests that a selection of higher functioning HCT survivors with a relatively better quality of life participated in this long-term follow-up study of stem cell transplantation survivors. These results could also impact the results of other long-term follow-up studies in cancer survivors, knowing that possibly an unhealthier population is missed in these studies and some long-term negative effects of treatments might be underestimated.