RESUMO
In the liver of adult mice bearing an Ehrlich carcinoma on the leg, progressively hypoxic and displaying reactive hepatitis but not metastatic dissemination, extramedullary hemopoiesis was detected. Electron microscopy revealed 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 hypoxic environments than the adult type. They were positive for the peroxidase reaction due to the presence of hemoglobin and could furthermore be visualized by the blue-excited red autofluorescence of protoporphyrin IX. Extramedullary hemopoiesis, one of the various examples of reactivation of fetal features in the liver associated with carcinogenesis, is supposed to be compensatory for the loss of blood cells induced by the tumor. Reviewing this process has the purpose of raising the question whether the fetal features are better adapted than adult ones to the metabolic and physiological characteristics of a tumor-influenced organism.