( CNN ) -- Five years after battling and beating breast cancer , `` Good Morning America '' co-anchor Robin Roberts faces another dangerous health foe . `` I 've always been a fighter , and with all of your prayers and support , a winner , '' Roberts said in an online message Monday . Roberts , 51 , was diagnosed with myelodysplastic syndrome , also called MDS , on the same day in April that her show beat out NBC 's `` Today Show '' in the ratings for the first time in nearly 16 years , she said . `` 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 , '' Roberts said . `` 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 . '' MDS is `` a disease of the blood and bone marrow and was once known as preleukemia , '' Roberts said in her message on the ABC News website . The Chart : What is preleukemia or MDS ? It can be brought on by chemotherapy and radiation , treatments that Roberts underwent after her breast cancer diagnosis . `` Sometimes the treatment for cancer can cause other serious medical problems , '' She said . `` My doctors tell me I 'm going to beat this -- and I know it 's true , '' Roberts said . While information found online about MDS can be `` some scary stuff , '' Roberts said her doctors told her it does n't apply to her . `` They say I 'm younger and fitter than most people who confront this disease and will be cured . '' Her sister , Sally-Ann Roberts , told New Orleans television station WWL -- where she is an anchor -- that the ABC host `` is not going through this journey alone . '' Her family is behind her , she said , and `` The best news that we received was that I 'm a match -- a perfect match . '' `` When I got that news , it was like Christmas times 1,000 , because anyone who knows what it 's like to wait for that kind of news realizes the trauma , '' she said . `` If Robin had not found a match within her family , she would have been one of those 6,000 people to be searching for a match . '' That search is conducted largely through the National Marrow Donor Program , which maintains a registry of bone-marrow donors . Sally-Ann Roberts said her sister is hoping to draw attention to the registry and encourage people to join . `` It 's very simple to be part of the registry , '' she said . `` I just had a swab , a cheek swab , and they test that and that 's how they determine that . '' Robin Roberts said marrow donors `` are scarce and particularly for African-American women , '' she said . `` I am very fortunate to have a sister who is an excellent match , and this greatly improves my chances for a cure . '' The announcement , made online and on her ABC show , came Monday because she is starting chemotherapy treatments in preparation for the transplant , she said . She posted a Twitter message Monday afternoon : `` Just got home from first treatment . All went well . My family & I are comforted by your prayers , love & support . See you in the morn '' Roberts will `` miss a day here or there , '' but she will continue to work through her treatments , she said . `` 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 . '' She will `` miss a chunk of time '' when she has her bone marrow transplant , 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 said . `` In facing this new challenge , I ask humbly for more of your prayers and love -- as I will keep you in mine and update you regularly on my condition . '' Roberts began contributing to `` Good Morning America '' in 1995 and was promoted to co-anchor in 2005 . She previously was a sports reporter for ESPN and television stations in Atlanta , Nashville and Mississippi . She was a star player on the Southeastern Louisiana University women 's basketball team , where she earned a communications degree in 1983 . CNN 's Joe Sutton contributed to this report .
NEW : ABC host 's sister says she 's a `` perfect match '' for a marrow transplant . ` ` Good Morning America '' co-anchor Robin Roberts faces MDS diagnosis . The disease attacks blood and bone marrow . It is the most common form of leukemia, but it can also be caused by other cancers or infections. she writes .