Enrollment in cancer treatment trials did not decrease substantially during the first year of the COVID-19 pandemic in the United States, according to a study published in JAMA Network Open.  

Although there were large reductions in cancer trial enrollments overall, the reductions appeared to occur primarily in control and prevention (CCP) trials, not in treatment trials.

In a cohort study, researchers examined initial enrollments in cancer treatment and CCP trials conducted by the SWOG Cancer Research Network from January 2016 through February 2021. Specifically, the researchers examined time points from the “onset” of the pandemic (March 1-April 25, 2020) and the “apex” (October 4, 2020-January 23, 2021).

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Overall, 29,398 patients were enrolled: 24,034 before the pandemic and 5364 during the pandemic. The majority of enrollments (66.2%) were to treatment trials.

During the onset of the pandemic, there was a 9.0% model-estimated weekly reduction in cancer trial enrollment compared with the pre-pandemic period (relative risk [RR], 0.91; 95% CI, 0.89-0.93; P <.001).

After the initial wave, enrollment recovered but decreased again in winter 2020 to 2021, during which period there was a 2.0% model-estimated weekly reduction in enrollments (RR, 0.98; 95% CI, 0.97-0.99; P <.001).

“Our findings also show how enrollment to clinical trials rebounded strongly after the initial wave of the pandemic,” the study authors wrote. “Although enrollment decreased again during the most severe COVID-19 wave of the winter of 2020 to 2021, the reduction was fairly modest.”

For both trial types, actual enrollment was 77.3% of expected enrollment during the pandemic. Actual enrollment was 54.0% of expected for CCP trials and 91.0% of expected for treatment trials.

The weekly relative reduction in enrollments during the initial wave of the pandemic was more than twice as high for CCP trials as it was for treatment trials (16.0% vs 6.0%; P <.001). During the apex, the relative reduction was similar for CCP and treatment trials (3.0% vs 2.0%; P =.74).

“Remarkably, over the full year of the pandemic, there was no strong evidence of a reduction in enrollments to treatment trials,” the authors wrote. “This may have occurred at the expense of full support of CCP trials, for which enrollment over the entire pandemic year was much lower.”

“If so, this pattern could reflect institutional prioritization of resources to target the conduct of trials most directly related to patient care and also could reflect that clinical research has rapidly adapted to the circumstances of enrolling and treating patients on protocols during the COVID-19 pandemic,” the authors concluded.

Disclosures: One study author declared an affiliation with a pharmaceutical company, and one declared an affiliation with a health benefits company. Please see the original reference for a full list of disclosures.


Unger JM, Xiao H, LeBlanc M, Hershman DL, Blanke CD. Cancer clinical trial participation at the 1-year anniversary of the outbreak of the COVID-19 pandemic. JAMA Netw Open. 2021;4(7):e2118433. doi:10.1001/jamanetworkopen.2021.18433