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Background: Older adults represent a large oncologic demographic and are under-represented within oncology research despite constituting nearly two-thirds of the oncologic population in the United States. Because many social factors influence research participation, those who enroll in research do not reflect the oncology population at large, introducing bias and creating issue with external validity of studies. The same factors that influence study enrollment may also impact cancer outcomes, meaning that those who enroll in studies may already have an improved chance of cancer survival, further skewing results of these studies. This study evaluates characteristics that influence study enrollment in older adults and explore to what degree these factors may influence survival after allogeneic blood or marrow transplantation.
Methods: This retrospective comparison study evaluates 63 adults aged 60 and above undergoing allogenic transplantation at one institution. Patients who elected and declined enrollment in a non-therapeutic observational study were evaluated. Demographic and clinical characteristics between groups were compared and assessed as predictors of transplant survival, including decision to enroll in the study.
Results: Participants who chose to enroll in the parent study were not different with regard to gender, race/ethnicity, age, insurance type, donor age, and neighborhood income/poverty level compared to patients who were invited to participate but declined enrollment. The research participant group had higher proportion assessed as being fully active (23.8% vs. 12.7%, p = 0.034) and lower mean comorbidity scores (1.0 vs 2.47, p = 0.008). Enrollment in an observational study independently predicted transplant survival (HR = 0.316, 95% CI 0.12-0.82, p = 0.017). When controlling for relevant confounders of disease severity, comorbidities, and transplant age, enrolling in the parent study was associated with a lower hazards of death following transplant (HR = 0.302, 95% CI 0.10-0.87, p = 0.027).
Conclusions: Despite being demographically comparable, persons who enrolled in one non-therapeutic transplant study had significantly improved survivorship than those who did not participate in observational research. These findings suggest that there are unidentified factors that influence study involvement that may also impact disease survivorship, over-estimating outcomes from these studies. Results from prospective observational studies should be interpreted with the consideration that study participants have an improved chance of survival at baseline.
