A study published in The Oncologist found that patients who enroll in clinical trials for treatment experience a heavy travel burden.

The study analyzed the data of 1,600 patients who enrolled in a clinical trial between 1993 and 2014, measuring the distance they traveled from their home to the site of the study and finding that, overall, patients traveled a median distance of 25.8 miles.

Patients in NIH-sponsored studies had to go even greater distances, 39.4 miles on average, and patients in phase 1 studies had to travel farther than any other type, traveling a median of 41.2 miles to participate, the study said.

“Future work will need to examine the total out-of-pocket expenses assumed by patients across multiple academic centers to account for regional and geographic variability of trial participation,” the study authors said.