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Imatinib mesylate (STI571) is a very effective treatment option for Ph(+) chronic myeloid leukemia (CML) in chronic phase. Secondary treatment failures have mostly been observed in patients with advanced stages of disease. We report the case of a patient who unexpectedly experienced blast crisis of the central nervous system although having achieved complete cytogenetic remission in the bone marrow. The levels of STI571 and its metabolite N-desmethyl STI were 40-fold lower in the cerebral spine fluid than in plasma. The risk of CNS disease has to be kept in mind when patients with CML in chronic phase who are at an increased risk for blastic transformation are treated with imatinib mesylate.

Isolated central nervous system (CNS) relapse occurred in 5 out of 24 patients (20.8%) with chronic myeloid leukemia (CML) lymphoid blast crisis (2), Philadelphia (Ph) chromosome positive acute lymphoblastic leukemia (ALL) (2) or CML with biphenotypic markers (1) treated on imatinib mesylate (IM) protocols at our institution. CNS relapse occurred despite peripheral blood (5) and bone marrow (3) complete responses. Median time to CNS relapse was day 32 (range 23 to 100). This observation raised the possibility that IM may not penetrate into the CNS. Simultaneous plasma and cerebral spinal fluid (CSF) IM levels were determined in four subsequent patients by liquid chromatography and mass spectrophotometric assay. Levels of IM were found to be approximately two logs lower in CSF than in plasma (0.044 microg/ml (0.088 +/- 0.029 micrro) vs 3.27 microg/ml (6.54 +/- 0.93 microM)). CSF levels were substantially below the concentration required for inhibition of BCR-ABL and killing of cell lines in vitro. These results suggest that IM may not penetrate the intact blood/brain barrier and its implications are discussed.

We report a 53-year-old man with lymphoid blast crisis of Ph+ chronic myeloid leukaemia who was treated with STI571, a selective inhibitor of the enzymatic activity of BCR-ABL. He responded excellently to STI571 (600 mg/d), obtaining a complete cytogenetic remission after 3 months of therapy. Although remission in the bone marrow was sustained, the patient developed an isolated central nervous system relapse. Subsequent analyses of STI571 concentrations in the cerebrospinal fluid (CSF) revealed 2-log lower CSF levels of STI571 than corresponding plasma levels. These are the first data demonstrating a low penetration of orally administered STI571 into the CSF in humans.