ABC News President Ben Sherwood sent out the following note this morning about Robin Roberts:

I'm afraid I have some tough news to share news this morning.

With courage and humanity, Robin beat breast cancer five years ago.

In a few minutes on GMA, she will share that she's facing a serious new health challenge.

The note from Robin, copied below, details her diagnosis and what it means. We love Robin, the heart and soul of ABC News, and we'll stand arm in arm with her as she fights this new battle. She is the captain of our GMA team; she has been the keystone of our recent victories; and she will lead the program for many years to come. Ben

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Here we go again…

As many of you know, 5 years ago I beat breast cancer. I've always been a fighter, and with all of your prayers and support, a winner.

Sometimes the treatment for cancer can cause other serious medical problems. Today, I want to let you know that I've been diagnosed with MDS or myelodysplastic syndrome. It's a disease of the blood and bone marrow and was once known as preleukemia.

My doctors tell me I'm going to beat this - and I know it's true.

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.

Today, I will start what is known as pre-treatment - chemotherapy in advance of a bone marrow transplant later this year. Bone marrow donors are scarce and particularly for African-American women. I am very fortunate to have a sister who is an excellent match, and this greatly improves my chances for a cure. As you know from my recent interview with Mark Zuckerberg, organ donation is vitally important. Many people don't realize they can be bone marrow donors. I encourage everyone to sign up on a donor registry like bethematch.org.

I received my MDS diagnosis on the very day that Good Morning America finally beat the Today Show for the first time in 16 years. Talk about your highs and lows! Then a few weeks ago, during a rather unpleasant procedure to extract bone marrow for testing, I received word that I would interview President Obama the next day. The combination of landing the biggest interview of my career and having a drill in my back reminds me that God only gives us what we can handle and that it helps to have a good sense of humor when we run smack into the absurdity of life.

Bottom line: I've been living with this diagnosis for awhile and will continue to anchor GMA. I love what I do and the people with whom I do it. Along with my faith, family and friends, all of you at ABC News give me the motivation and energy to face this challenge.

Going forward, it's business as usual at GMA, which means I'll be right here every day with George, Sam, Josh and Lara. When I miss a day here or there, I'm fortunate that some very talented friends at ABC News will fill-in. When I undergo the transplant later this year, I'll miss a chunk of time.

When I faced breast cancer, your prayers and good wishes sustained me, gave me such hope and played a major role in my recovery. 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.

Love and blessings,

Robin