Five years ago, celebrated television anchor Robin Roberts beat breast cancer, but Monday on Good Morning America, Roberts revealed that she has myelodysplastic syndrome (MDS) -- a type of bone marrow disease with around 12,000 new cases diagnosed each year, according to the American Cancer Society.

What is MDS?
Also called preleukemia, myelodysplastic syndrome is a group of conditions in which blood cells do not reach a mature state, staying in the bone marrow. When these defective cells outnumber healthy cells, multiple problems like anemia, rapid bleeding or severe infection can develop.

Causes
If doctors do not know the underlying causes of the patient's condition, it is called a de novo MDS.

If the cause is known, it is called secondary MDS. Smoking and exposure to certain chemicals (like benzene) increase one's risk. Cancer treatment like chemotherapy and radiation are a common cause.