Investigating residual leukemic cells in acute lymphoblastic leukemia: a practical approach using a streamlined interphase fluorescence in situ hybridization method on cerebrospinal fluid.

Introduction: A precise diagnosis of central nervous system involvement in acute lymphoblastic leukemia (ALL) requires comprehensive knowledge of morphological analysis, with a focus on the quantity and quality of cells being examined. Some research has utilized techniques such as immunocytochemistry, flow cytometry, polymerase chain reaction (PCR), and interphase fluorescence in situ hybridization (iFISH) on cerebrospinal fluid (CSF) cytospin samples to detect any remaining leukemic cells in the CSF. To obtain reliable results using immunocytochemistry and flow cytometry, it is essential to use freshly collected specimens within a limited timeframe. At the same time, PCR requires a sufficient number of cells for DNA extraction. On the other hand, the iFISH procedure on CSF cytospin samples can be challenging and requires practice. Therefore, there is a need for a fast, easy method that will be affordable and marketable in laboratories where the above methods are not available, or the sample is insufficient to use those methods.

Methods: The samples were prepared by centrifugation of 1 mL aliquots of CSF collected into EDTA tubes. The CSF sample was centrifuged at 3000 rpm for 3 min, the supernatant was removed, and the pellet was placed in KCl hypotonic solution for 5 min at 37 °C. Other steps (fixation, hybridization, wash steps, and analysis) were the same as in the standard protocol for blood samples. The BCR-ABL1 rearrangements were performed and evaluated in 200 interphase cells.

Results: 90% of Ph(+) cells were found in CSF.

Conclusion: We propose a significantly streamlined iFISH method for detecting blast/residual leukemic cells in acute lymphoblastic leukemia using CSF as a complementary test option.