Erythroid progenitors in tumor-bearing mice: erythroid inhibitory factors produced by adenocarcinoma-755.

Adenocarcinoma-755-bearing C57BL/6 mice developed anemia with the growth of the tumors. The numbers of granuloid and monocytoid progenitors (colony-forming unit in culture, CFU-C) of the bone marrow and spleen and the peripheral blood WBC counts increased in tumor-bearing mice. The erythroid progenitors (erythroid colony-forming units, CFU-E; erythroid burst-forming units, BFU-E) of the bone marrow showed a marked decrease, overcoming their increase in the spleen in tumor-bearing mice. Fractionation of conditioned medium of tumor cells led to the isolation of a protein of 80-kd molecular weight that stimulated murine CFU-C growth and inhibited the CFU-E and BFU-E growth in a dose-dependent manner. These results indicate that erythroid inhibitory factors produced by tumors exist in tumor-bearing mice. Erythroid inhibitory factors might also exist in non-hematological malignancies of humans, and they might be one of the mechanisms of anemia.