Robin Roberts already beat breast cancer in 2007, and now she faces another fight for her life. The Good Morning America anchor told viewers Monday that she has been diagnosed with myelodysplastic syndroms, or MDS, a rare blood disorder that attacks the body's bone marrow. Roberts told viewers that the disease is a complication from her breast cancer treatment, and while the diagnosis is grim for most sufferers, doctors are optimistic that she'll beat it. "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!" she wrote in a blog post on GMA's Web site. She'll continue to co-anchor the show until fall when she will receive a bone marrow transplant with the help of her sister, Sally-Ann, who is a perfect match for Roberts. "I am very fortunate to have a sister who is an excellent match, and this greatly improves my chances for a cure," she said. "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 wrote in her blog. "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."