“Good Morning America” anchor Robin Roberts announced on Monday (Jun 11) that she is suffering from a rare blood disorder known as myelodysplastic syndrome (or “MDS” for short).

The 51-year-old will undergo a bone marrow transplant this summer with her sister as a donor. She says she learned about her diagnosis on the day of a major milestone for ABC: the day the network received news that after 16 years, GMA had beaten NBC’s “Today” show in viewer ratings.

“Talk about your highs and lows!” Roberts said. She continued in her statement, “My doctors tell me I’m going to beat this – and I know it’s true.”

When asked by co-host Lara Spencer what her colleagues could do for her, Roberts responded, “You crave normalcy when you go through this because nothing is normal anymore. I need pop news, I need sports! I need you to be who you are, what you are. This too shall pass.”

It was only 5 years ago that Roberts beat breast cancer, and the cancer treatment is what may have triggered the MDS in her system.

Roberts begins treatment this week, and she will receive a drug to prepare her for the bone marrow transplant. Once complete, she will be off the air for a few months to recover.

Read the letter Robin sent out to her colleagues explaining her condition below:

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

Our thoughts and prayers definitely go out to Robin Roberts, and here’s to her beating this disease — just like she beat cancer — as well as a speedy recovery!