[Masked Philadelphia chromosome: diagnostic implications in a case of chronic myeloid leukemia presenting in blast crisis].

We present a female patient with acute non-lymphoblastic leukemia (ANLL) and with haematologic features suggestive of its evolution from chronic myeloid leukaemia (CML), in which a bone marrow karyotype showing a "masked" Philadelphia (Ph) chromosome due to a variant translocation of complex type t(9;9;22)(q32;q34;q11) was found. We comment the peculiarities of this special Ph chromosome as well as the differential diagnostic problems between ANLL Ph(+) and CML with onset in blastic crisis.