Bone marrow is the spongy material inside bones. It is full of the youngest type of blood cells—called stem cells—from which all other blood cell types develop (white blood cells, red blood cells, and platelets). Stem cells are also found in circulating (also called peripheral) blood, although in a much less concentrated form.

There are different types of stem cell transplants. When peripheral blood is used as a source of stem cells for a transplant, it is called a peripheral blood stem cell transplant or PBSCT. If the child does not have cancer cells in the bone marrow, as is usually the case for children with solid tumors, the child usually is able to donate his own stem cells for a transplant. This type of transplant is called an autologous PBSCT, and this chapter deals specifically with this type of stem cell transplant.

In an autologous PBSCT, the number of stem cells in the blood are increased by giving children a drug called granulocyte colony-stimulating factor (G-CSF). The G-CSF is given as a shot under the skin. It is typically started 24 hours after chemotherapy, and continued until the stem cell collection has been completed.

The stem cells are collected in a procedure called apheresis. These cells can be stored for months or even years. When a child is admitted to the hospital for the transplant procedure, high doses of chemotherapy drugs that are known to be effective against the type of tumor they have are administered. These very high doses kill more tumor cells, but they also prevent the bone marrow from producing stem cells. The child’s own stem cells are then given back to the child via a central venous catheter (e.g., Hickman^® catheter). See the section titled “Stem cell harvest and storage” later in this chapter for a description of the collection and storage process.

The transplant can be done one or more times, allowing doctors to expose the tumor cells to high doses of chemotherapy while limiting toxicity and the risk of life-threatening infections. When this process is done more than once, it is called tandem PBSCT, serial PBSCT, or sequential PBSCT.