RESUMEN
Hematogones, which are normal precursors of B lymphocytes in the bone marrow, may be mistaken for blast cells on flow cytometry and histology when their numbers increase. We report such a case in a 16 months old male who was unsuccessfully treated for a pre-B cell ALL on the basis of flow cytometry of the bone marrow which showed a substantial population of CD19 and CD10 expressing 'blast' cells. A diagnosis of AML M7 was made on a subsequent bone marrow biopsy in which the blast cells expressed CD61 and Factor VIII, while they were negative for CD10 and CD20. Also present were a few CD10 and CD20 expressing small lymphoid cells, which were interpreted as hematogones. This report reiterates the problem of mistaking hematogones for 'blast' cells on flow cytometry, especially in the marrow of very young children where hematogones are often prominent.