Robin Roberts, of ABC, has blood, bone marrow disorder

NEW YORK (AP) -- Robin Roberts is facing a new medical challenge that will require her to start chemotherapy and get a bone marrow transplant.

   The "Good Morning America" anchor announced on the ABC show Monday morning that she has been diagnosed with myelodysplastic syndrome, a blood and bone marrow disease once known as preleukemia.

   She says she will undergo chemo and a bone marrow transplant this year as "pretreatment" for the disease, which she says she has known about for several weeks. She says her sister is a great match for her. While she says she'll miss a day here and there, she'll remain on the air.

   Roberts battled breast cancer five years ago.