Identification of circulating melanoma cells in uveal melanoma patients by dual-marker immunoenrichment

Purpose. Despite successful local tumor control, uveal melanoma (UM) patients may develop lethal metastases. To reliably identify circulating melanoma cells (CMC) in UM patients, we set out to test a new immunomagnetic enrichment assay and screened UM patients for the presence of CMC. We also determined whether we could find CMC in culture; for example, for future drug testing. Methods. A dual-immunomagnetic enrichment assay using antibodies against two melanoma markers (NKI/C3 and NKI/beteb) was used to determine the presence of UM cells in blood. The sensitivity of the assay was determined by spiking normal blood with 92.1 cells (concentration range, 1-10⁴ cells/mL). Isolated cells were characterized by immunocytochemistry directly after immunoenrichment and after a 2-week culture. The presence of CMC was determined in the peripheral blood of 31 patients with UM, and results were compared to clinical prognostic factors at the time of presentation. Results. The CMC were detected in 93.5% (n1/429 of 31) of the patients with primary nonmetastatic UM at a median density of 3.5 cells/10 mL blood (range, 0-10.2 cells), as well as in blood cultures. No significant association was observed between the presence or number of CMC and any clinical prognostic factors. Conclusions.The improved dual-immunoenrichment assay enabled the detection of intact and viable CMC in the majority of UM patients. We also were able to identify CMC after short-term culturing. Molecular characterization of the CMC rather than the prevalence of these cells is expected to provide relevant information on the individual risk of metastasis.