Metastatic carcinoma with carcinocythemia mimicking leukemia.

Carcinoma metastatic to the bone marrow may present with peripheral blood and bone marrow changes and a clinical picture difficult to distinguish from leukemia. It is important to make an accurate diagnosis since the management is different. We have described a patient with circulating primitive cells and diffuse marrow involvement by similar cells. The pathologic process may be identified without cell markers by careful attention to the pattern of distribution, as well as the cytologic features of the neoplastic cells in the bone marrow biopsy.