Squamous cell carcinomas (SCC) originate from epithelial tissues in various organs across the body and are associated with exposure to environmental carcinogens such as tobacco, alcohol or ultraviolet radiation. Despite the overlapping histopathological features and driver mutations, SCCs from different anatomic sites have different prognoses. Oral and lung SCC are highly invasive and metastatic, whereas cutaneous SCC (cSCC) are seldom fatal and have a metastasis rate of approximately 2%. As fibroblast are key cells in the microenvironment and are critical for epithelial cell development and differentiation, we examined how fibroblasts from different tissues contribute to differences in SCC outcomes.

Utilising normal human fibroblast and SCC cell lines from the skin, lung, and head and neck we modelled with in vitro organotypic models how fibroblasts and SCCs interact in a tissue specific manner to drive invasion and proliferation. Mechanisms were explored with lipidomics, RNA sequencing and validated in vivo. We validated our data in patient samples using spatial transcriptomics of clinical samples and analysis of public clinical cohorts.

We discovered that fibroblasts contribute to SCC aggressiveness in a tissue-specific manner by modulating SCC proliferation and invasion. Oral and lung fibroblasts enhance SCC invasion by inducing epithelial-to-mesenchymal transition, whereas dermal fibroblasts lack this effect, aligning with the low metastatic potential of cSCC. Lipidomic profiling revealed distinct metabolic interactions between fibroblasts and SCCs. Oral fibroblasts transfer sphingomyelins, activating the ceramide/S1P/STAT3 pathway to drive oral SCC invasion, while lung fibroblasts supply triglycerides, fuelling cholesterol synthesis and promoting aggressive lung SCC behaviour. In contrast, dermal fibroblasts exhibit low lipid content, corresponding to the reduced invasiveness of cSCC. Blocking fibroblast lipid metabolism, SCC lipid uptake, or lipid processing suppressed oral and lung SCC invasion, highlighting potential therapeutic targets. Spatial transcriptomics and patient cohort analysis confirmed the presence of these fibroblast-epithelial lipid interactions in clinical samples and their correlation with SCC outcomes. Notably, these interactions were evident in early-stage lesions, suggesting a role in SCC initiation and progression.

Our study establishes fibroblasts as key regulators of SCC progression through tissue-specific lipid metabolism. By shaping the tumour microenvironment, fibroblasts drive SCC aggressiveness in an anatomic site-dependent manner. These findings open avenues for targeting fibroblast-derived lipid pathways to prevent or mitigate SCC progression, with potential implications for early intervention and precision therapies.