Carcinocythemia (carcinoma cell leukemia) due to metastatic carcinoma of the breast: report of a case.

A patient with a 17-year course of metastatic lobular carcinoma of the breast is described who developed large numbers of circulating carcinoma cells which were easily detectable in several routine peripheral blood smears shortly before death. This rare complication of carcinoma has been called "carcinocythemia." Carcinocythemia is probably due to widespread infiltration of many bone marrow sites and may also be related to splenectomy, which may impair reticuloendothelial clearance of circulating tumor cells. The differential diagnosis of carcinocythemia from superimposed acute myelogenous leukemia, which can complicate radiotherapy and chemotherapy for the primary tumor, is discussed. Cytomorphology, histochemistry, and electron microscopy of abnormal circulating cells should aid in the distinction of these two processes.