In a rare move, NASA is cutting a mission aboard the International Space Station short after an astronaut had a medical issue.

The space agency said Thursday the U.S.-Japanese-Russian crew of four will return to Earth in the coming days, earlier than planned.

NASA canceled its first spacewalk of the year because of the health issue. The space agency did not identify the astronaut or the medical issue, citing patient privacy. The crew member is now stable.

NASA officials stressed that it was not an onboard emergency, but are "erring on the side of caution for the crew member," said Dr. James Polk, NASA's chief health and medical officer.

Polk said this was NASA's first medical evacuation from the space station although astronauts have been treated aboard for things like toothaches and ear pain.