Some hematologic (blood-based) cancers and specific types of solid tumors are best treated with very high doses of chemotherapy and/or radiation. But the doses necessary for killing the tumor may also destroy healthy bone marrow. This would be life-threatening, because without healthy bone marrow, your body could not produce the red cells, white cells, and platelets that carry oxygen throughout your body, fight infection, and cause your blood to clot after an injury.
So, before you begin treatment, your own healthy blood stem cells, also called hematopoietic cells, are collected at a time when there is little disease in the bone marrow, and then frozen for future use. The process is similar to a blood donation. (Think of blood stem cells as seeds that can both divide to produce more healthy blood cells, and transform themselves into the three types of blood cells—red cells, white cells, and platelets.)
Your bone marrow and the abnormal (cancer) cells inside you are then destroyed with chemotherapy and/or radiation in a process called dose-intensive therapy. In the next step, called the rescue, your marrow or blood stem cells that were collected previously will be thawed and given back to you intravenously. They travel through your bloodstream and back into your bone marrow, where they can start producing healthy blood cells again.