Hemopoiesis in the liver of adult tumor-bearing mice

in the liver of adult mice bearing an Ehrlich carcinoma on the leg, progres sively hypoxic and displaying reactive hepatitis but not metastatic dissemi nation, extramedullary hemopoiesis was detected. Electron microscopy reveal ed mainly erythropoietic islands and scattered megakaryocytes in maturation stages up to the platelet-releasing phase. Erythropoietic cells expressed an embryonic-type of hemoglobin, which is more adequate to oxygenate hypoxi c environments than the adult type. They were positive for the peroxidase r eaction due to the presence of hemoglobin and could furthermore be visualiz ed by the blue-excited red autofluorescence of protoporphyrin IX, Extramedu llary hemopoiesis, one of the various examples of reactivation of fetal fea tures in the liver associated with carcinogenesis, is supposed to be compen satory for the loss of blood cells induced by the tumor. Reviewing this pro cess has the purpose of raising the question whether the fetal features are better adapted than adult ones to the metabolic and physiological characte ristics of a tumor-influenced organism.