Isolation and characterization of circulating melanoma cells by size filtration and fluorescent in-situ hybridization

Isolation of circulating tumor cells (CTCs) from blood of melanoma patients has been difficult owing to inconsistent expression of surface antigens. Here we report on the isolation, detection, and characterization of CTCs from blood of melanoma patients using microfiltration and fluorescent in-situ hybridization (FISH). Two tubes of blood from 15 patients with advanced melanoma were collected. These two tubes subsequently underwent filtration through a membrane with pore sizes of 7.5 μm. Isolated cells from one tube were analyzed by FISH for RREB1 (6p24), MYB (6q32), SE6 (D6Z1), and CCND1 (11q13) and the other paired specimen was analyzed by immunofluorescence for HMB45, melanoma-associated antigen recognized by T cells-1, tyrosinase and melanogenesis associated transcription factor. We identified CTCs in 10 out of 13 melanoma samples by immunofluorescence (2.5-99 CTCs/3 ml of blood) and in 13 specimens by FISH (7.2-76 CTCs/3 ml of blood) with more CTCs identified by FISH in 10 out 13 samples. Two filters failed. Our results show that CTCs are detectable in the majority of patients with advanced melanoma. These tools will be useful in characterizing treatment related changes of melanoma in CTCs.