Determining the Sensitivity and Specificity of Circulating Tumor Cells and Cytology in Cerebrospinal Fluid of Patients Clinically Suspected for Leptomeningeal Metastases

Leptomeningeal metastases (LM), is a diffuse dissemination of tumor cells into the cerebrospinal fluid (CSF) and leptomeninges.[1] Up to 8% of all patients with cancer develop LM. Gadolinium enhanced MRI of the symptomatic location of the nervous system is the radiological method of choice when LM is clinically suspected. In patients with a metastasized tumor, based on clinical signs of LM and contrast enhancement of either the leptomeninges, pia mater/cortex or cranial or spinal nerves on MRI, the diagnosis LM can be made. The sensitivity of MRI with gadolineum for LM is 75% and the specificity 77%. If MRI does not show equivocal abnormalities, CSF cytology needs to be performed. In 55% of patients with LM from solid tumors, malignant cells are found during the first CSF examination. The sensitivity raises to 80-90% after the second CSF sampling, as determined in the pre-MRI era. The volume of sampled CSF determines partly the sensitivity of CSF cytology. If possible, 10 ml CSF needs to be taken and the material must be processed as quickly as possible.

Recently, Patel et al (2011) described the detection of breast cancer cells in the CSF using the Cell Search System (Veridex). [6] Using this method, the CSF is enriched immuno-magnetically for the epithelial cell adhesion molecule (EpCAM). Next nuclear staining with 4 ',6-diamidino-2-phenylindole (DAPI) and immunofluorescent detection with cytokeratin and CD45 is performed in 5 patients with leptomeningeal metastases from breast cancer and approximately 104 circulating tumor cells (CTCs)in 7,5 ml CSF were found, using this method. There seemed to be an association between the number of CTCs and response to intrathecal administered chemotherapy in this small group of patients.

In the future, the determination of CTCs in the CSF could be a new quantitative method for the anti-tumor response assessment of systemic or intrathecal therapy (as opposed to CSF cytology, which is subjective and not a quantitative method). If the method shows greater sensitivity than CSF cytology and can reliably measure single tumor cells, the sensitivity of CSF examination in patients with a clinical suspicion of LM will increase. Possibly, this method can also be used to detect micrometastases in the CSF in patients without neurological symptoms, but with a high risk of CNS metastases.