A leader on the Metropolitan Washington Airports Authority board, which oversees Dulles International and Reagan National airports as well as the $6 billion rail to Dulles project, has resigned.

Mame Reiley told Gov. Bob McDonnell she was stepping down because of “a health challenge” in a letter dated Feb. 15. Reiley is currently battling breast cancer.

“It has become abundantly clear to me that my priorities need to shift so that I may concentrate my time on my health, my family, and my work,” Reiley wrote.

Reiley has been a key player on the board since she was appointed in 2002. She was a fierce advocate for an underground station at Dulles airport for the new Silver Line. But the board scuttled that idea last year after protests from local leaders worried about the project’s escalating costs.

McDonnell has not yet announced a replacement for Reiley.

Reiley’s resignation was first reported by The Washington Post