Laser-induced breakdown spectroscopy (LIBS) was recently introduced as a rapid bone analysis technique in bone-infiltrating head and neck cancers. Research efforts on laser surgery systems with controlled tissue feedback are currently limited to animal specimens and the use of nontumorous tissues. Accordingly, this study aimed to characterize the electrolyte composition of tissues in human mandibular bone-infiltrating head and neck cancer. Mandible cross-sections from 12 patients with bone-invasive head and neck cancers were natively investigated with LIBS. Representative LIBS spectra (n = 3049) of the inferior alveolar nerve, fibrosis, tumor stroma, and cell-rich tumor areas were acquired and histologically validated. Tissue-specific differences in the LIBS spectra were determined by receiver operating characteristics analysis and visualized by principal component analysis. The electrolyte emission values of calcium (Ca) and potassium (K) significantly (p < 0.0001) differed in fibrosis, nerve tissue, tumor stroma, and cell-rich tumor areas. Based on the intracellular detection of Ca and K, LIBS ensures the discrimination between the inferior alveolar nerve and cell-rich tumor tissue with a sensitivity of ≥95.2% and a specificity of ≥87.2%. The heterogeneity of electrolyte emission values within tumorous and nontumorous tissue areas enables LIBS-based tissue recognition in mandibular bone-infiltrating head and neck cancer.

Head and neck mucosal melanoma (HNMM) arises in the nasal and oral cavities and has the propensity to metastasize to local and distant body sites. HNMM is also notable for its resistance to available therapeutics. The rarity of this disease makes it difficult to conduct large-scale clinical studies to develop standard treatment protocols. In contrast to cutaneous melanoma, c-Kit-dependent pathways are well studied in HNNMM and provide a potential therapeutic target. We identified and isolated genetically distinct subpopulations with stem cell characteristics in HNMM samples bearing Kit wild-type and mutations. Functional analysis of these subpopulations reveals that, in addition to expressing the stem cell marker proteins CD20, CD117, CD133, and CD166, these subpopulations are characterized by self-renewal potential, migratory capacity, and resistance to Kit inhibitors such as Imatinib. Immunofluorescence staining and inhibition experiments demonstrate that the maintenance and resistance of HHMM subpopulations to Kit inhibitors is mediated by the Kit signal to the PI3K signaling pathway. The KIT signal to the PI3K signaling pathway does not result exclusively from a KIT mutation localized to Exon 17, but can also be triggered by mutations localized to Exons 11 and 13. In the present study, we identify and characterize an HNMM subpopulation with stemness properties in patients with c-Kit wild-type and mutation, and demonstrate for the first time the mechanisms by which the CD117⁺/CD133⁺ HNMM subpopulations survive and confer resistance to the specific inhibitor of c-Kit mutation.