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Most blood cells in the body develop from cells in the bone marrow – the spongy material in the center of the bones --- called stem cells. Stem cells mature into different kinds of blood cells, each with its own special job: White blood cells help fight infection, red blood cells carry oxygen to tissues throughout the body, and platelets help form blood clots to control bleeding. These blood cells are created as the body needs them. Normally, when cells grow old or get damaged, they die, and new cells take their place. However, sometimes this process can go wrong. Cells do not grow and divide normally, or the immune system goes haywire and attacks normal tissue.
In a person with leukemia, for example, the bone marrow makes abnormal white blood cells, called leukemia cells. Unlike normal blood cells, leukemia cells don't die when they should. They may crowd out normal white blood cells, red blood cells and platelets, making it difficult for normal blood cells to do their work.
Myeloproliferative disorders begin in the bone marrow and may cause a greater than normal number of stem cells to develop into one or more types of blood cells. The disorders usually get worse slowly as the number of extra blood cells slowly increases.
In lymphoma, abnormal cells in the lymphatic system divide and grow without order or control or old cells do not die normally. Because lymphatic tissue is present in many areas of the body, non-Hodgkin's lymphoma can start almost anywhere.
Non-Hodgkin's lymphoma may occur in a single lymph node, a group of lymph nodes, or an organ and can spread to almost any part of the body. Over time, lymphoma cells may replace the normal cells in the bone marrow.
Myeloma develops when the body overproduces plasma cells. Normally, certain white blood cells leave the bone marrow and mature in other parts of the body. Some of these develop into plasma cells that produce proteins called antibodies that move through the bloodstream to help the body get rid of harmful substances. Because the body has many types of plasma cells, it can respond to many substances. When cancer involves plasma cells, the body keeps producing more and more of these cells. The unneeded plasma cells--all abnormal and all exactly alike--are called myeloma cells. They can collect in the bones and form tumors or cause other problems.
Myelodysplastic Syndrome (MDS) refers to a group of disorders in which the bone marrow produces too few mature and/or functioning red blood cells, white blood cells or platelets. It begins with a change to a normal stem cell in the bone marrow.