Requirement for written informed consent and selection bias in a chart-review prostate cancer study

Although retrospective chart-review studies are typically performed using a waiver of written informed consent, many institutional review boards (IRB) do not approve such waivers for chart-review studies using prospective enrollment, which could introduce selection bias in participant characteristics and outcomes, thereby impairing representativeness and validity. We aim to determine this bias in a chart-review prostate cancer (PCa) study using prospective enrollment. Using an IRB-approved chart-review protocol with a waiver of written informed consent for prospective enrollment, we identified 2202 patients scheduled for initial prostate biopsy from 2007 to 2021 at Durham Veterans Affairs Healthcare System. These patients were simultaneously approached for enrollment into a separate minimal-risk prospective observational study protocol requiring blood collection and written consent. One thousand two hundred thirty-eight subjects provided written consent to the blood collection protocol; 964 did not. Patients who provided written consent differed in several key characteristics, including younger age, but had a similar racial distribution. Importantly, participants providing written consent had a significantly lower risk of PCa (multivariable OR = 0.41; 95% CI, 0.31-0.54; P < .001). As such, patients who provided written consent had younger age, similar race, and lower PCa risk and therefore might not accurately represent the full eligible population. To minimize selection bias, a waiver of written consent should be allowed for chart-review studies using prospective enrollment.