Cutaneous squamous cell carcinoma (cSCC) is the leading cause of death in recessive dystrophic epidermolysis bullosa (RDEB) patients but remains poorly studied on a proteomic level. We aim to characterize the RDEB-SCC proteome by comparing it to the proteomes of UV-light induced cSCC of non-aggressive and aggressive behavior with which RDEB cSCC share either the well-differentiated morphology or the aggressive behavior, respectively. We applied a direct trypsinization protocol using an acid labile surfactant and label-free quantitation to study formalin-fixed, paraffin-embedded tissues from patients with RDEB cSCC (n=6), low-risk cSCC (n=5) and metastasizing cSCC (n=13) by liquid chromatography tandem-mass spectrometry.