Comparative skin cancer atlas and interactome: A multi-modal spatial approach to uncovering the cells and interactions underlying skin cancer diversity

The three major skin cancer types - squamous cell carcinoma (SCC), basal cell carcinoma (BCC), and melanoma - account for >70% of all cancer. Although these cancers all derive from the outer skin layer (epidermis), variability in cell type composition and interactions causes substantial cross-cancer differences in disease initiation and invasive and metastatic potential. A knowledgebase of cell type composition and cell-to-cell interactions within the three skin cancers is needed to aid the assessment of risks and prognosis upon patient presentation. Here we integrated six distinct yet complementary spatial single-cell technologies to build the largest cell atlas and interactome of SCC, BCC, and melanoma to date. First, we performed single-cell RNA sequencing (scRNAseq) on >50,000 cells from 11 paired healthy and SCC patient biopsies. GeoMx spatial proteomics data independently validated the presence of rare immune cell types defined by scRNAseq. Visium and CosMx transcriptomic analyses were performed for all three skin cancer types to map spatial neighbourhoods and construct a cell-to-cell interaction atlas. We independently validated two key LR interactions, PD1_PDL1 and IL34_CSF1R, using Opal Multiplex Polaris and RNAscope data. Downstream analysis of IL34_CSF1R signalling zones suggested enrichment of IL34-related antigen presenting pathways in melanoma. Overall, we present a valuable database and analysis approaches to reveal potential biomarkers of initiation and progression of the most lethal type (melanoma) and the most common types (SCC and BCC) of skin cancer. Overall design: Overall, samples from 12 human skin cancer patients were profiled by spatial and single cell multi-omics. Adjacent tissue sections from the same tissue blocks (FFPE - Formalin Fixed Paraffin Embedded blocks, or OCT- Optimal Cutting Temperature blocks) were used.