Stem cell transplantation

High dose chemotherapy with peripheral blood stem cell transplantation is a procedure used with increasing frequency for certain well defined types of cancer. The procedure involves using much higher dosages (amounts) of chemotherapy than would normally be used, thereby obtaining a much greater response in terms of killing the cancer cells.

As explained earlier, one of the problems with chemotherapy is that it decreases the function of the cells in the bone marrow. Stem cells are cells found in normal bone marrow that are the originating cells that divide to form any of the other cells found in the bone marrow and in the blood. Therefore, if some of the stem cells can be taken out of the body during the chemotherapy treatment, the risk of using higher doses of chemotherapy is much less, as the stem cells can be replaced after the treatment to rebuild the bone marrow.

The patient is given medicines that stimulate the stem cells to reproduce much faster than normal, so much so that many of them 'overflow' the bone marrow and can be found in the patient's blood. A special machine called a cell separator is used to take the stem cells out of the blood where they can be kept (like a unit of blood) in a fridge. The process on the cell separator machine takes about three to four hours, and looks very much like a kidney dialysis machine - blood is removed continually from the patient's vein, the stem cells are removed to the bag, and the rest of the blood is then pumped back into the patient's vein. All of this happens continuously, so that there is never more than about 50 - 100ml of blood out of the patient's body at any one time (less than one cup full).

As soon as the stem cells have been harvested from the blood, the chemotherapy is administered. This usually takes about six to eight hours, and is given overnight in the hospital. Twenty-four hours after the chemotherapy has finished, the stem cells are given back to the patient in the form of a blood transfusion, taking about 30 - 45 minutes. After this, the patient may be discharged, depending on how close they live to the hospital, and how well they have reacted to the treatment.

Side-effects

Because the doses of chemotherapy that are used in this procedure are higher than those used normally, the side effects are also more frequent and severe. The biggest problem that occurs following this procedure is that of neutropenia (a very low white cell count), and very low platelet counts. The white cells are the cells in the blood that help your body to fight infections and the platelets help with clotting.

During the time that the white cells are very low after high dose chemotherapy, patients are at a very high risk of developing infections. Because the immune system is at such a low status, any infection needs to be treated aggressively and as soon as possible. Therefore, any patient with neutropenia and a fever or infection needs to be admitted to hospital and started on antibiotic treatment within hours of it developing.

Patients admitted to hospital with infection and neutropenia after stem cell transplant may need to remain there for between two to six weeks, as the low blood counts can persist for that long. In addition, most patients will require platelet transfusions and blood transfusions following this treatment.