Tion and kept on ice in a PBS solution until ESR analysis.Human Paraffin-embedded Tissue Sections112 human paraffin embedded melanoma and nevus specimens were prepared as previously described [31,32]. Two experimental sets were analyzed: 26 paraffin-embedded specimens (40 microns slides) of human nevus or melanoma (13 nevi and 13 melanomas) were assigned to the “Measuring set” and were analyzed first. Then a second independent set of 86 paraffin-embedded specimens (47 nevi and 39 melanomas) was assigned to the “Validation set” and analyzed. ESR measurements were carried out according to the methodology reported below. Paraffin embedded slices were weighed and ESR data were all normalized accordingly. Slice of pure paraffin revealed no ESR signal.Methods Cell CulturesFive human melanoma cell lines from both primary and Solvent Yellow 14 metastatic melanomas were purchased from the American Type Culture Collection (ATCC, Manassas, VA) and cultured according to the manufacturer’s instructions. SKMEL-28 (ATCC number HTB-72), SKMEL-2 (ATCC number HTB-68) and amelanotic C32 (ATCC number CRL-1585) cell lines were grown in Eagle’s 
Minimum Essential Medium (EMEM) with FBS to a final concentration of 10 . SKMEL-31 cell line (ATCC number HTB-73) was grown in EMEM with FBS to a final concentration of 15 ; SKMEL-3 cell line (ATCC number HTB-69) was grown in McCoy’s 5a medium with FBS to a final concentration of 15 . SKMEL-110 human metastatic melanoma cells [4] 
were a kind gift of Dr. Cirielli (IDI-IRRCS, Rome) and were grown in Dulbecco’s modified Eagle’s medium (DMEM) with FCS to a final concentration of 10 . NHEM-neo primary melanocytes (Cambrex) were grown in MBM-2 supplemented with MGM-4 SingleQuots (CaCl2, FGF-2, PMA, rh-Insulin, Hydrocortisone, bovine pituitary extract (BPE), FBS and Gentamicin/Amphotericin) (Cambrex, Charles city). Normal Human Umbilical Vein Endothelial Cells (HUVEC) were from Lonza Inc. (Walkersville, MD) and were grown in Endothelial Cell Basal MedChemExpress K162 Medium-2 (Clonetics/BioWhittaker Inc., Charlotte, NC) supplemented with: Hydrocortisone, hFGF-2, VEGF, R3-IGF-1, Ascorbic Acid, Heparin, FBS, hEGF, GA-1000 (Clonetics/BioWhittaker, Inc., Charlotte, NC). Human adult low Calcium Temperature keratinocytes (HaCaT) were a kind gift of Dr. Pastore (IDI-IRRCS, Rome) [30] and were grown in DMEM medium with FBS 10 final concentration. Cells were grown in 75 cm2 flasks and media was changed every other day. Once a 75 confluence was reached, cells were trypsinized, harvested by centrifugation (10 minutes at 1500 RPM), washed and transferred into glass flat capillaries. ESR analysis was performed on intact cells; viability assay by trypan blue exclusion test always indicated at least 98 of live cells. Commercially available melanoma cells were used at maximum fifth passage, unless differently specified.Ethics StatementThe data were collected within a study approved by the local Ethic Committee (IDI IRCCS and San Carlo Hospital Ethical Committee Protocol, July 19th 2005; Reg. N. 154); written informed consent was obtained and all data were analyzed anonymously.ESR AnalysisFor ESR spectra on intact cells, signals were recorded using 80ml samples in flat glass capillaries (inner dimensions 0.464.0 mm)to optimize instrument sensitivity as previously described for cells in aqueous suspension. [33] Measurements on cells were performed at room temperature with an ESP300 X-band instrument (Bruker, Karlsruhe, Germany) equipped with a high sensitivity TM110-mode c.Tion and kept on ice in a PBS solution until ESR analysis.Human Paraffin-embedded Tissue Sections112 human paraffin embedded melanoma and nevus specimens were prepared as previously described [31,32]. Two experimental sets were analyzed: 26 paraffin-embedded specimens (40 microns slides) of human nevus or melanoma (13 nevi and 13 melanomas) were assigned to the “Measuring set” and were analyzed first. Then a second independent set of 86 paraffin-embedded specimens (47 nevi and 39 melanomas) was assigned to the “Validation set” and analyzed. ESR measurements were carried out according to the methodology reported below. Paraffin embedded slices were weighed and ESR data were all normalized accordingly. Slice of pure paraffin revealed no ESR signal.Methods Cell CulturesFive human melanoma cell lines from both primary and metastatic melanomas were purchased from the American Type Culture Collection (ATCC, Manassas, VA) and cultured according to the manufacturer’s instructions. SKMEL-28 (ATCC number HTB-72), SKMEL-2 (ATCC number HTB-68) and amelanotic C32 (ATCC number CRL-1585) cell lines were grown in Eagle’s Minimum Essential Medium (EMEM) with FBS to a final concentration of 10 . SKMEL-31 cell line (ATCC number HTB-73) was grown in EMEM with FBS to a final concentration of 15 ; SKMEL-3 cell line (ATCC number HTB-69) was grown in McCoy’s 5a medium with FBS to a final concentration of 15 . SKMEL-110 human metastatic melanoma cells [4] were a kind gift of Dr. Cirielli (IDI-IRRCS, Rome) and were grown in Dulbecco’s modified Eagle’s medium (DMEM) with FCS to a final concentration of 10 . NHEM-neo primary melanocytes (Cambrex) were grown in MBM-2 supplemented with MGM-4 SingleQuots (CaCl2, FGF-2, PMA, rh-Insulin, Hydrocortisone, bovine pituitary extract (BPE), FBS and Gentamicin/Amphotericin) (Cambrex, Charles city). Normal Human Umbilical Vein Endothelial Cells (HUVEC) were from Lonza Inc. (Walkersville, MD) and were grown in Endothelial Cell Basal Medium-2 (Clonetics/BioWhittaker Inc., Charlotte, NC) supplemented with: Hydrocortisone, hFGF-2, VEGF, R3-IGF-1, Ascorbic Acid, Heparin, FBS, hEGF, GA-1000 (Clonetics/BioWhittaker, Inc., Charlotte, NC). Human adult low Calcium Temperature keratinocytes (HaCaT) were a kind gift of Dr. Pastore (IDI-IRRCS, Rome) [30] and were grown in DMEM medium with FBS 10 final concentration. Cells were grown in 75 cm2 flasks and media was changed every other day. Once a 75 confluence was reached, cells were trypsinized, harvested by centrifugation (10 minutes at 1500 RPM), washed and transferred into glass flat capillaries. ESR analysis was performed on intact cells; viability assay by trypan blue exclusion test always indicated at least 98 of live cells. Commercially available melanoma cells were used at maximum fifth passage, unless differently specified.Ethics StatementThe data were collected within a study approved by the local Ethic Committee (IDI IRCCS and San Carlo Hospital Ethical Committee Protocol, July 19th 2005; Reg. N. 154); written informed consent was obtained and all data were analyzed anonymously.ESR AnalysisFor ESR spectra on intact cells, signals were recorded using 80ml samples in flat glass capillaries (inner dimensions 0.464.0 mm)to optimize instrument sensitivity as previously described for cells in aqueous suspension. [33] Measurements on cells were performed at room temperature with an ESP300 X-band instrument (Bruker, Karlsruhe, Germany) equipped with a high sensitivity TM110-mode c.