Detection of malignant cells in cerebrospinal fluid using fluorescence in situ hybridization

Cytologic examination of cerebrospinal fluid (CSF) is the diagnostic gold standard for leptomeningeal metastasis (LMM). However, this technique is only moderately sensitive when routine staining procedures are applied. The use of fluorescence in situ hybridization (FISH) to identify malignant cells may have an additional value in diagnosing LMM, since numerical chromosomal aberrations (NCA) can be detected at the single cell level. We tested the feasibility of FISH to detect tumor cells in CSF by analyzing 22 samples with proven LMM with a probe for chromosome 1 (1q12) to detect NCA in the cells. A control group consisted of samples from 10 patients with inflammatory neurologic disease. In 7 LMM samples no cells or only lysed cells were found, due to time delay before fixation. Of the other 15 LMM samples analyzed, 13 showed NCA (87%), while no NCA were found in the control group. Our results indicate that FISH may be a useful additional diagnostic tool to the cytodiagnosis of CSF in cases of LMM. We expect that FISH can become an additional marker for malignancy at the single cell level in patients with LMM, which may also be of use to determine the effect of therapy for LMM.