Circulating melanoma cells and survival in metastatic melanoma

A validated assay for the enumeration of circulating melanoma cells (CMCs) may facilitate the development of more effective therapies for metastatic melanoma patients. In this study CD146(+) cells were immunomagnetically enriched from 7.5 ml of blood. Isolated cells were fluorescently stained with DAPI, anti-molecular weight melanoma-associated antigen (HMW-MAA). anti-CD45 and CD34 and Ki67. CMCs were identified as CD146(+), HMW-MAA(+), CD45(-), CD34(-), Ki67(-/+) cells. Eighty-eight percent of spiked SK-MEL28 cells in 7.5 ml blood were recovered. In all 55 healthy donors <= 1 CMCs were detected in 7.5 ml of blood. A retrospective analysis was conducted comparing CMC counts and overall survival in 79 blood samples from 44 melanoma patients. CMCs ranged from 0 to 8,042 per 7.5 ml. Two or more CMCs were detected in 18 (23%) of the patients and 30-100% (mean 84%) of the CMCs expressed the proliferation marker Ki6.7. Patients with >= 2 CMCs per 7.5 ml of whole blood, as compared with the group with < 2 CMCs, had a shorter overall survival (2.0 months vs. 12.1 months, P=0.001).