Suppressive effects of an extramedullary tumor on bone marrow erythropoiesis and stroma.

Mice, bearing a solid extramedullary Ehrlich ascites tumor developed anemia, reticulocytosis, and leukocytosis after 3 weeks of tumor growth. Erythopoiesis in the marrow, as measured by erythroblast counts and radioiron uptake of the humerus and femur, was suppressed to less than 30% of normal. However, striking erythroblastic and granulocytic hyperplasia in the spleen occurred to compensate for suppression of erythropoiesis in the marrow. Accompanying the medullary erythropoietic insufficiency was a similar suppression to 30% of normal in the growth of bone marrow stromal colonies in vitro. The fact that erythropoiesis was suppressed in the marrow, but not in the spleen, and bone marrow stromal colony growth was concomitantly suppressed, suggest that a change in the cellular component of the hemopoietic microenvironment had occurred. Splenectomy, prior to tumor inoculation, did not ameliorate the anemia. However, removing this potentially compensatory site for erythropoiesis prevented the severe suppression of erythroblast counts and stromal colony growth from the marrow. Thus, it appeared that, with sufficient stimulus, the suppression of erythropoiesis in the marrow was preventable.