Stimulation Tests for the Bone Marrow Neutrophil Pool in Malignancies

It has been known for decades that blood neutrophilia occurs after the administration of etiocholanolone, adrenocortical steroids, and endotoxins. Neutrophil leukocytosis in general may be due to several mechanisms such as increased stimulation of the myelopoiesis, increased release from the marrow, a shift from the marginated to the circulating pool (demargination), prolongation in the peripheral half-life, and decreased migration of neutrophils from the blood to the tissue. However, the principal cause of the neutrocytosis for each of the above mentioned agents is increased release of neutrophils from the bone marrow reserves. Since a sufficient reserve capacity is a prerequisite for optimal defenses against infections, the marrow response has been used to estimate the dose of chemotherapy expected to be tolerated without life-threatening neutropenia. However, none of the above "test substances" have gained widespread use due to adverse reactions or undesirable effects on neutrophil function. Recent progress in biotechnology has developed recombinant human (rh) hematopoietic growth factors ready for clinical use. Marrow myelopoiesis is stimulated by granulocyte colony-stimulating factor (rhG-CSF) and granulocyte-macrophage CSF (rhGM-CSF). The immediate effect, however, is mobilization of mature neutrophil granulocytes to the blood. Bone marrow cellularity seems to influence the neutrophil number mobilized during 24 hours by one subcutaneous injection of either rhG-CSF or rhGM-CSF. A recent pilot study has suggested such a "24 hour stimulation test" to predict severe neutropenia following cyclic chemotherapy. This concept is illustrated by two case reports. The "stimulation test" suggests that we may devise strategies to define patient subsets which may benefit from prophylactic growth factor administration during cyclic chemotherapy.