Cytogenetic and molecular characterization of a masked Philadelphia chromosome in chronic myelocytic leukemia

A case of typical chronic myeloid leukemia with an apparently Philadelphia-negative karyotype is described. Molecular studies confirmed the cytogenetic interpretation of a standard Ph rearrangement, with secondary involvement of 22q- in a translocation with chromosome #5, leading to its masking. The chromosomal regions engaged in the standard t(9;22) were not modified and the molecular rearrangements of Ph were also conserved. The hematologic and clinical features were apparently not influenced by the events leading to the masking of Ph. Further similar observations with both cytogenetic and molecular characterization are needed to better identify the possible clinical consequences of these complex changes.