Circulating Melanoma Cells (CMCs) in Mucosal and Uveal Melanomas Khoja L1,2,3, Shenjere P2, Bramley S1, Milner R4, Kvist A4, Califano R2, Clack G4, Hughes A4, Lorigan P2,3, Dive C1,3 1Clinical and Experimental Pharmacology Group, Paterson Institute for Cancer Research, Manchester, UK; 2The Christie NHS Foundation Trust, Manchester, UK; 3School of Cancer and Enabling Sciences, University of Manchester, Manchester Cancer Research Centre and Manchester Academic Health Sciences Centre, Manchester, UK; 4AstraZeneca Pharmaceuticals, Alderley Park, SK10 4TG, UK Background Melanoma subtypes are increasingly defined by genetic alterations (BRAF mutations in 50% and NRAS in 20% of cutaneous, c-Kit aberrations in acral and mucosal and GNA11 mutations in uveal melanomas. CMCs are a potential biomarker to predict and assess response to treatment, monitor disease relapse and provide new targets for drug development. Methods The CellSearch (Veridex USA) and ISET (Isolation by Size of Epithelial Tumour Cells,Rarecells, France) platforms were evaluated for CMC detection in 23 prospectively recruited patients. CellSearch detected CMCs in 6/11 mucosal (range 1-125, mean 21 median 1) and 7/10 uveal (range 1-510, mean 57 median 3) melanomas. MART-1 was used as an additional CMC kit detection marker . MART-1 positive CMCs were detected in both subtypes but circulating tumour microemboli (CTM) were found only in mucosal melanomas. Immunohistochemistry with CD45/ CD144 (leukocyte and endothelial markers) and S100 (melanoma marker) identified CMCs with characteristic staining and morphology. Examples of CMCs detected by CellSearch A and B CTM and single CMCs in 2 mucosal patients , C single CMC in a uveal patient CellSearch (marker dependent) ISET (marker independent) 8µm pore leukocyte Examples of CMCs (and contaminating cells) on ISET. A endothelial cells B S100+ CTC in uveal patient C S100+ CTC in uveal patient, D,E S100+CTC and S100- CTCs in sinonasal mucosal patient Results Table 1: Patient Demographics CTCs detected by CellSearch, during dacarbazine chemotherapy, are pharmacodynamic Comparison of the platforms in 20 patients showed no correlation suggesting they detect different CMC populations (Spearman’s correlation p=0.17). ISET detected CMCs in 10/12 mucosal (range 1-26, mean 4 median 2) and 7/10 uveal (range 1-19, mean 7 median 3) melanomas. CMCs were both S100+ and S100-. No CTM were detected. Conclusions This is the first report of CMC detection by CellSearch in mucosal and uveal melanomas. Comparison with ISET revealed no relationship between numbers of CMCs detected in the same patients by each platform thus indicating significant CMC heterogeneity in CMC marker expression and size. Circulating tumour microemboli may indicate collective cell migration thus probing the biology of metastases formation. lkhoja@yahoo.com