What are Colony Stimulating Factors (CSFs)?
White cells, red cells and platelets are produced in the bone marrow in a constant production line, to replace the cells that are old and dying. The life expectancy of each of these cell lines ranges from 10 days to 3 months. The bone marrow is a busy place.
Under normal circumstances, there are feedback signals (CSFs) to regulate fresh production, increasing production when required. G-CSF causes a rise in the white cell count in case of an infection. When the red cell count goes down (anemia), signals (erythropoietin) try to boost production. In the past few years, a new kind of medicine has become available, which mimics the signal to boost platelet production (thrombopoietin mimetics).
Diseases, organ damage, chemotherapy and radiation therapy to sensitive spots affect this production line. E.g. in kidney failure, the kidneys are not able to produce the hormone required to keep up red cell production, and patients need injections of erythropoietin to treat their anemia.
Chemotherapy kills cells in the production line, and causes a decline in blood counts. The bone marrow then catches up, but there is a lag time. In that period, patients are vulnerable to infections. Some chemotherapy drugs are more potent than others in this regard, and some patients (frail, elderly, or with other major medical issues) are more vulnerable. To help the bone marrow recover faster, we use G-CSF (Neupogen, Neulasta, etc) injections after each chemotherapy treatment. In select circumstances, these have been shown to decrease the need for hospitalizations for fevers related to low white cell counts. These are mainly used during curative treatment, when it is relatively important to keep to a set schedule, and not have to delay therapy. For metastatic disease, in most circumstances, it is more beneficial to reduce doses, or increase intervals and give the bone marrow a better chance to recover on its own. We also avoid G-CSF during radiation therapy, as there has been shown a decrease in radiation efficacy.
In cases of chemotherapy related anemias, injections of erythropoietin (brand name Procrit, etc) are used to boost red cell production and decrease the need for blood transfusions. These came to be used very widely in the first few years of availability, with advertisements of happy grandparents having the energy to keep up with their grandchildren, while getting chemotherapy. The pressure was on to raise the red cell count up to normal, thinking that was going to eliminate the problem of chemotherapy related fatigue. I remember having many disagreements with sales representatives in those days.
In fact, in the last decade, we have found many risks to administering erythropoietin above a certain level of hemoglobin. The FDA has added a black box warning to that effect, and started a program of getting informed consent before the initiation of such treatments. We have also been advised to avoid erythropoietin during curative chemotherapy, as there is a statistical risk of decreasing survival. It is not clear whether this is due to the CSFs, or due to a poor underlying medical condition.
In general, we have learnt to use CSFs in more appropriate circumstances. The FDA regularly reviews its recommendations as they track adverse effects.