Interphase Fluoroscence in Situ Hybridization Improves the Detection Rate of CNS Involvement in Childhood Acute Lymphoblastic Leukemia.

Morphologic examination of CSF cytospin is the standard method in the detection of CNS involvement of childhood acute lymphoblastic leukemia (ALL). However, the result widely varies depending on the status of cell degeneration caused by cytospin procedure. We performed interphase fluoroscence in situ hybridization (FISH) on CSF cytospin cells to examine its potential usefulness in detecting malignant cell population in the CSF.

The study used 19 CSF cytospin specimens of the childhood ALL patients under treatment. All of them had cytogenetic abnormalities in the bone marrow nuclear cells at the initial diagnosis. None of the patients showed malignant cells in morphologic examination of the cytospin. Interphase FISH was performed to detect recurrent genetic abnormalities including rearrangement of BCR/ABL, TEL/AML1, MLL and IgH rearrangement, and p16 deletion using LSI BCR/ABL dual color, dual fusion translocation probe, LSI TEL/AML1 ES dual color translocation probe, LSI MLL dual color, break apart rearrangement probe, LSI IGH dual color, break apart rearrangement probe, and LSI p16/CEP 9 dual-color probe (Abbot Molecular Diagnostics). FISH signals were interpreted using automated slide scanning system (Metafer 4 system) and manually read for confirmation.

Two patients had the same cytogenetic abnormalities in CSF cytospin as observed in the bone marrow mononuclear cells: one patient had 4 copies of AML1 gene, suggesting tetrasomy 21 or multiple fusion partner gene other than chromosome 12, both in bone marrow and in CSF; the other had 3 copies of p16 gene including one with low signal intensity both in bone marrow and in CSF. Ten patients did not have any cytogenetic abnormalities. We could not interpret the result in the other 7 patients due to low cell count and/or low signal intensity.

Out of 19 who were diagnosed not to have malignant cell in CSF in morphologic examination, 2 patients had cells with the same clonal abnormalities in the CSF as bone marrow. Our result indicates that FISH study would be helpful in evaluating CSF involvement of hematologic malignancies including ALL. In order to improve the performance, it is required to prevent degeneration of the cells by prompt specimen delivery and slide preparation.

No relevant conflicts of interest to declare.