06/11/2012 at 11:25 AM EDT
Robin Roberts is facing another health scare.
The Good Morning America
anchor revealed Monday that she is battling MDS, or myelodysplastic syndrome
, a disease of the blood and bone marrow – and that she will have a bone-marrow transplant, with her sister as a donor.
"My doctors tell me I'm going to beat this – and I know it's true," Roberts, 51, writes in an emotional message to fans
on the GMA
"If you Google MDS, you may find some scary stuff, including statistics that my doctors insist don't apply to me. They say I'm younger and fitter than most people who confront this disease and will be cured."
Roberts, who beat breast cancer
several years ago, will begin chemotherapy immediately.
The bone-marrow transplant will happen later this year. "I am very fortunate to have a sister who is an excellent match, and this greatly improves my chances for a cure," she says.
She expects to miss "a chunk of time" after the transplant, but hopes to keep working at GMA
full time, or close to it, until then.
"I love what I do and the people with whom I do it," she says. "Along with my faith, family and friends, all of you at ABC News give me the motivation and energy to face this challenge."
Roberts, who leaned on her sisters
during her battle against breast cancer as well, suggested Monday that her cancer treatments were likely the cause of this new medical problem. Still, she is optimistic she'll make a full recovery.
"When I faced breast cancer, your prayers and good wishes sustained me, gave me such hope and played a major role in my recovery," she says. "In facing this new challenge, I ask humbly for more of your prayers and love – as I will keep you in my mine and update you regularly on my condition."