E metastatic stage, and increasing incidence worldwide. [1] Melanoma accounts for about 4 of skin cancers, causing however about 80 of skin cancerrelated deaths in western countries. Despite promising recent improvement at the therapeutic level, [2?] surgical excision remains at this moment the most effective treatment at early stages, while therapeutic interventions have weak efficacy at advanced phases due to high metastatic potential and resistance to currently available therapies. [7]. Improving early diagnosis may therefore strongly affect melanoma-related mortality. Melanoma diagnosis routinely starts from non-invasive dermatoscopy- and epiluminescence-based skininspection, to identify phenotypic features of the pigmented lesion. [8] Trained dermatologists still experience significant error-rate giving misdiagnosis and delay in treatment, and formal diagnosis still requires to be confirmed by histological analysis. [9] Hence, alternative non-invasive Epigenetic Reader Domain procedures are needed to improve the early non-invasive diagnostic accuracy. Several reports indicate melanogenesis as a key process in the melanoma biology. [10,11] Melanin synthesis involves an oxidation/reduction reactions chain leading to the synthesis of final organic polymers. The intermediate free radicals formed within such process [12] give melanin paramagnetic properties. [13] Besides free radicals, melanin may also contain or interact with metal ions and paramagnetic gases (dioxygen, nitric oxide) which also contribute to its paramagnetic properties. [14] ESR spectroscopy is the technique of choice to detect and to investigate freeMelanoma Diagnosis via Electron Spin Resonanceradicals. As such, it has long been used in melanin basic research since melanin ESR signal is Epigenetic Reader Domain stable, [15?7] resistant to chemical degradation, [18] and different in eumelanin from pheomelanin. [19,20]. Previous studies investigated ESR spectra of melanoma tissues under 15755315 different conditions, [21?9] including formaline fixed-, or frozen-, or paraffin-embedded specimens. However, a large study investigating ESR spectra in human melanoma specimens compared to human nevus specimens is still lacking at this moment. The main goal of the present study was to provide strong support to the use of 
ESR spectroscopy as a reliable diagnostic help in melanoma management. To this aim we identified an endogenous ESR signal (g = 2.005) in melanoma and nonmelanoma human cell lines, then investigated this signal in mouse melanoma tissues. Finally, we investigated ESR signal in human melanoma specimens compared to human nevus specimens. A specific ESR signal was found in melanoma human tissues, significantly different from the one recorded in nevus paraffinembedded specimens; ROC analysis showed that ESR signal is able to discriminate human melanoma sections from nevi, with very high accuracy.In vivo Mouse Melanoma ModelFor in vivo mouse experiments, murine B16F10 melanoma cells were purchased from American Type Culture Collection (ATCC, Manassas, VA) (ATCC number CRL-6475) and grown in DMEM (Hyclone, Logan, UT) with 10 FCS (Hyclone, Logan, UT) [5]. Media were completed by the addition of 
glutamine (2 mM) and penicillin/streptomycin (50 U/ml- 50 mg/ml) (Gibco, Carlsbad, CA). Cells were grown at 37uC with 5 CO2 and subsequently injected in the dorsal skin of 20 weeks-old male C57BL/6 mice (number of animals = 5) according to a previously reported procedure [4]. Primary melanomas were removed 2 weeks after cell-inocula.E metastatic stage, and increasing incidence worldwide. [1] Melanoma accounts for about 4 of skin cancers, causing however about 80 of skin cancerrelated deaths in western countries. Despite promising recent improvement at the therapeutic level, [2?] surgical excision remains at this moment the most effective treatment at early stages, while therapeutic interventions have weak efficacy at advanced phases due to high metastatic potential and resistance to currently available therapies. [7]. Improving early diagnosis may therefore strongly affect melanoma-related mortality. Melanoma diagnosis routinely starts from non-invasive dermatoscopy- and epiluminescence-based skininspection, to identify phenotypic features of the pigmented lesion. [8] Trained dermatologists still experience significant error-rate giving misdiagnosis and delay in treatment, and formal diagnosis still requires to be confirmed by histological analysis. [9] Hence, alternative non-invasive procedures are needed to improve the early non-invasive diagnostic accuracy. Several reports indicate melanogenesis as a key process in the melanoma biology. [10,11] Melanin synthesis involves an oxidation/reduction reactions chain leading to the synthesis of final organic polymers. The intermediate free radicals formed within such process [12] give melanin paramagnetic properties. [13] Besides free radicals, melanin may also contain or interact with metal ions and paramagnetic gases (dioxygen, nitric oxide) which also contribute to its paramagnetic properties. [14] ESR spectroscopy is the technique of choice to detect and to investigate freeMelanoma Diagnosis via Electron Spin Resonanceradicals. As such, it has long been used in melanin basic research since melanin ESR signal is stable, [15?7] resistant to chemical degradation, [18] and different in eumelanin from pheomelanin. [19,20]. Previous studies investigated ESR spectra of melanoma tissues under 15755315 different conditions, [21?9] including formaline fixed-, or frozen-, or paraffin-embedded specimens. However, a large study investigating ESR spectra in human melanoma specimens compared to human nevus specimens is still lacking at this moment. The main goal of the present study was to provide strong support to the use of ESR spectroscopy as a reliable diagnostic help in melanoma management. To this aim we identified an endogenous ESR signal (g = 2.005) in melanoma and nonmelanoma human cell lines, then investigated this signal in mouse melanoma tissues. Finally, we investigated ESR signal in human melanoma specimens compared to human nevus specimens. A specific ESR signal was found in melanoma human tissues, significantly different from the one recorded in nevus paraffinembedded specimens; ROC analysis showed that ESR signal is able to discriminate human melanoma sections from nevi, with very high accuracy.In vivo Mouse Melanoma ModelFor in vivo mouse experiments, murine B16F10 melanoma cells were purchased from American Type Culture Collection (ATCC, Manassas, VA) (ATCC number CRL-6475) and grown in DMEM (Hyclone, Logan, UT) with 10 FCS (Hyclone, Logan, UT) [5]. Media were completed by the addition of glutamine (2 mM) and penicillin/streptomycin (50 U/ml- 50 mg/ml) (Gibco, Carlsbad, CA). Cells were grown at 37uC with 5 CO2 and subsequently injected in the dorsal skin of 20 weeks-old male C57BL/6 mice (number of animals = 5) according to a previously reported procedure [4]. Primary melanomas were removed 2 weeks after cell-inocula.
