This booklet begins with a brief description of normal blood and marrow, provided for background, followed by a detailed description of MDS and its treatment. It includes a glossary to help readers understand medical terms. Some of the medical terms used throughout this booklet may be synonyms for other words or phrases used by healthcare professionals. For example, MDS has been known as "smoldering leukemia," "preleukemia" or "oligoleukemia."
MDS originates from mutations in a normal stem cell (a multipotential hematopoietic cell) in the marrow (see Figure 1, page 4). With MDS, blood cell production in the marrow is usually increased and the marrow becomes filled with more than the normal number of developing blood cells. The blood is usually deficient in cells because the developing cells in the marrow die as they approach maturity, before they would normally be released into the blood. This leads to reduction in the number of circulating red cells (anemia), neutrophils (neutropenia) and platelets (thrombocytopenia).