[Thrombocythemia with Philadelphia chromosome. Secondary appearance of chronic myeloid leukemia].

The finding of a Philadelphia chromosome in a case of apparently primary thrombocythaemia should change the diagnosis for that of chronic myeloid leukaemia. This theoretical view is supported by the case reported here, where a Philadelphia-chromosome was detected in the bone marrow cells of a patient with severe thrombocythaemia; a typical myeloid leukaemia developed 21 months after the onset of the disease; survival was of short duration.