Robin Roberts says she plans to take medical leave from "Good Morning America" this summer to undergo treatment for a bone-marrow disease.

The "GMA" anchor and breast-cancer survivor is battling myelodysplastic syndrome.

Roberts, 51, said Thursday she will take a medical leave in late August or early September to undergo a marrow transplant. It is unclear how long she will be gone.

"It's fascinating-slash-scary how to prepare yourself for something like this," the New York Daily News said Roberts told reporters in a Los Angeles press conference she participated in via satellite from New York.

Filling in for her while she is out on leave will be Barbara Walters, Diane Sawyer, Katie Couric and Kelly Ripa, ABC News President Ben Sherwood said.