Recessive dystrophic epidermolysis bullosa (RDEB) is a rare severe hereditary skin disease characterized by skin and mucosa fragility, resulting in blister formation. The most severe complication in RDEB patients is the development of cutaneous squamous cell carcinoma (SCC), leading to premature death. There is a great deal of evidence suggesting a permissive tumor microenvironment (TME) as a driver of SCC development in RDEB patients. In a cohort of RDEB patients, we characterized the immune profiles of RDEB-SCCs and compared them with clinical, histopathological, and prognostic features. RDEB-SCCs were subdivided into four groups based on their occurrence (first onset or recurrences) and grading according to clinical, histopathological parameters of aggressiveness. Thirty-eight SCCs from 20 RDEB patients were analyzed. Five RDEB patients experienced an unfavorable course after the diagnosis of the first SCC, with early recurrence or metastasis, whereas 15 patients developed multiple SCCs without metastasis. High-risk primary RDEB-SCCs showed a higher neutrophil-to-lymphocyte ratio in the tumor microenvironment and an increased proportion of neutrophil extracellular traps (NETs). Additionally, citrullinated histone H3, a marker of NETs, was increased in the serum of RDEB patients with high-risk primary SCC, suggesting that this modified form of histone H3 may serve as a potential blood marker of unfavorable prognosis in RDEB-SCCs.

Recessive dystrophic epidermolysis bullosa (RDEB) is a rare severe hereditary skin disease characterized by skin and mucosa fragility, resulting in blister formation. The most severe complication in RDEB patients is the development of cutaneous squamous cell carcinoma (SCC) leading to premature death. Multiple evidences suggest a permissive tumor micro-environment (TME) as driver of SCC development in RDEB patients. In a cohort of RDEB patients, we characterized the immune profiles of RDEB-SCCs and compared them with clinical, histopathological, and prognostic features. RDEB-SCCs were subdivided into 4 groups based on their occurrence (first onset or recurrences) and grading according to their clinical-histopathological parameters of aggressiveness. Thirty-eight SCCs from 20 RDEB patients were analysed. Five RDEB patients experienced an unfavorable course af-ter the diagnosis of the first SCC, with early recurrence or metastasis, whereas 15 pa-tients developed multiple SCCs without metastasis. High-risk primary RDEB-SCCs showed a higher neutrophil-to-lymphocyte ratio in the tumor microenvironment, and an increased proportion of neutrophil extracellular traps (NET). Additionally, citrullinated histone H3, a marker of NETs, was increased in the serum of RDEB patients with high-risk primary SCC, suggesting that this modified form of histone H3 may serve as a potential blood marker of unfavorable prognosis in RDEB-SCCs.

Pachyonychia congenita (PC) is a rare and painful skin disorder caused by dominant pathogenic variants in keratin genes (KRT6A/KRT6B/KRT6C/KRT16/KRT17), with no effective treatment. We developed a scalable, in-depth and miniaturized MS-based proteomics and phospho-proteomics analysis of full-thickness skin biopsies applied to 10 PC patients to elucidate pathogenic mechanisms and pinpoint therapeutic targets. We quantified 7200 Protein Groups (PGs) on average from 2mm snap-frozen skin samples, the most in-depth proteome coverage reported to date from a single-shot MS analysis. Among the identified PGs, ∼1400 proteins were differentially abundant in lesional vs. non-lesional samples. Enrichment analysis points towards impaired mitochondrial function, hyper-keratinization, enhanced immune response and a significant increase in cholesterol biosynthesis. Phosphoproteomics revealed hyper-phosphorylation of specific sites in PC-related keratins, confirmed the hyper-activation of EGFR and downstream kinases, including PKC and Src, and disclosed p38 MAPK activation. All of these kinases have been reported to phosphorylate keratins. Our study expands upon current understanding of the consequences of EGFR pathway activation, including increased cholesterol biosynthesis, thereby renewing interest in the use of statins for PC. Above all, it provides a solid foundation for the continued exploration of EGFR inhibitors and offers therapeutic avenues, particularly those using multikinase inhibitors.