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Peripheral stem cell transplantation, or peripheral stem cell support, is a process in which stem cells are collected from blood and given to a patient in order to replace missing bone marrow. It is often used during cancer treatment, particularly for patients with lymphoma or leukemia, because some high-dose radiotherapy and chemotherapy treatments can destroy bone marrow. In the final part of peripheral stem cell transplantation, stem cells are infused into the blood stream, where they travel to the bone marrow and develop into blood cells. The branch of medicine concerned with the blood is known as hematology.
Stem cells used in peripheral stem cell transplantation may be collected from a compatible donor, or from the patient before the start of cancer treatment. If the patient's own stem cells are not used, close relatives such as siblings are often the most suitable donors. This is because the risk of side effects, associated with the body rejecting a transplant, is lower when donated stem cells match the patient's own cells as nearly as possible.
The first part of peripheral stem cell transplantation involves a technique known as apheresis, which is used to extract stem cells from blood. Normally, stem cells are located in bone marrow, so drugs are given which stimulate the marrow to produce stem cells and release them into the circulation. The transplantation medicine is injected daily for a number of days before apheresis is carried out.
During the apheresis procedure, a tube called a catheter is inserted into a vein in the arm. Over a period of up to four hours, blood is drawn out through the catheter and flows into a machine which collects the stem cells. Leftover blood goes back to the patient through another catheter or through a second channel in the original tube. When cancer patients collect their own cells for peripheral stem cell transplantation the bone marrow may be suppressed and, if not enough stem cells are harvested, apheresis may need to be repeated. Sometimes additional drugs can be used to boost stem cell production.
Stem cells are normally frozen and stored until required. Once patients have completed their high-dose cancer treatments the stem cells are infused into a vein in a process resembling blood transfusion. This part of peripheral stem cell transplantation takes up to five hours. After reaching the bone marrow, stem cells develop into red and white blood cells and platelets.