Cancer-associated fibroblasts with distinct origins and functions establish a pro-tumorigenic environment in squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is a serious public health problem due to its high incidence and metastatic potential. It progresses from actinic keratosis (AK), a precancerous lesion, or the in situ carcinoma Bowen's disease (BD). During this progression, malignant keratinocytes activate dermal fibroblasts into tumor-promoting cancer-associated fibroblasts (CAFs), whose origin and emergence remain largely unknown. Here, we generated and analyzed >115,000 single-cell transcriptomes from healthy skin, BD and cSCC. Our results reveal immunoregulatory and matrix-remodeling CAF subtypes that could be traced to pro-inflammatory and mesenchymal fibroblasts, respectively. These CAFs are absent in AK, change their proportions along the cSCC continuum, and interact with different cell types to establish a pro-tumorigenic microenvironment. Notably, these findings were cSCC-specific and were not recapitulated with basal cell carcinomas. Our study provides novel insights into the origin and functionalities of dermal CAFs that will be highly beneficial for the specific targeting of cSCC microenvironment.