The keratinocyte carcinomas, basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC), are the most common cancers in humans. Recently, an increasing body of literature has investigated the role of miRNAs in keratinocyte carcinoma pathogenesis, progression and their use as therapeutic agents and targets, or biomarkers. However, there is very little consistency in the literature regarding the identity of and/or role of individual miRNAs in cSCC (and to a lesser extent BCC) biology. miRNA analyses that combine clinical evidence with experimental elucidation of targets and functional impact provide far more compelling evidence than studies purely based on clinical findings or bioinformatic analyses. In this study, we review the clinical evidence associated with miRNA dysregulation in KCs assessing the quality of validation evidence provided, identify gaps, and provide recommendations for future studies based on relevant studies that investigated miRNA levels in human cSCC and BCC. Furthermore, we demonstrate how miRNAs contribute to the regulation of a diverse network of cellular functions, and that large-scale changes in tumor cell biology can be attributed to miRNA dysregulation. We highlight the need for further studies investigating the role of miRNAs as communicators between different cell types in the tumor microenvironment. Finally, we explore the clinical benefits of miRNAs as biomarkers of keratinocyte carcinoma prognosis and treatment.

Cutaneous squamous cell carcinoma (cSCC) is the second most common malignancy worldwide, with most deaths caused by locally advanced and metastatic disease. Treatment of resectable metastases is typically limited to invasive surgery with adjuvant radiotherapy; however, many patients fail to respond and there is minimal data to predict response or propose effective alternatives. Precision medicine could improve this, though genomic biomarkers remain elusive in the high mutational background and genomic complexity of cSCC. A phenotypic approach to precision medicine using patient‐derived ex vivo tumour models is gaining favour for its capacity to directly assess biological responses to therapeutics as a functional, predictive biomarker. However, the use of ex vivo models for guiding therapeutic selection has yet to be employed for metastatic cSCC. This review will therefore evaluate the existing experimental models of metastatic cSCC and discuss how ex vivo methods could overcome the shortcomings of these existing models. Disease‐specific considerations for a prospective methodological pipeline will also be discussed in the context of precision medicine.

The keratinocyte carcinomas, basal cell carcinoma (BCC), and cutaneous squamous cell carcinoma (cSCC), are the most common cancers in humans. Recently, an increasing body of literature has investigated the role of miRNAs in keratinocyte carcinoma pathogenesis, progression and their use as therapeutic agents and targets, or biomarkers. However, there is very little consistency in the literature regarding the identity of and/or role of individual miRNAs in cSCC (and to a lesser extent BCC) biology. miRNA analyses that combine clinical evidence with experimental elucidation of targets and functional impact provide far more compelling evidence than studies purely based on clinical findings or bioinformatic analyses. In this study, we review the clinical evidence associated with miRNA dysregulation in KCs, assessing the quality of validation evidence provided, identify gaps, and provide recommendations for future studies based on relevant studies that investigated miRNA levels in human cSCC and BCC. Furthermore, we demonstrate how miRNAs contribute to the regulation of a diverse network of cellular functions, and that large-scale changes in tumor cell biology can be attributed to miRNA dysregulation. We highlight the need for further studies investigating the role of miRNAs as communicators between different cell types in the tumor microenvironment. Finally, we explore the clinical benefits of miRNAs as biomarkers of keratinocyte carcinoma prognosis and treatment.

Background/Objectives: Cutaneous squamous cell carcinoma (cSCC) is a very common skin malignancy of the head and neck area, with a propensity to spread to local lymph nodes. Epithelial-to-mesenchymal transition (EMT) and cancer-associated fibroblasts (CAFs) play a well-documented role in the progression of the disease. In this study, we developed and characterised multicellular tumour spheroids (MCTS) composed of patient-derived metastatic cSCC cell lines—each exhibiting distinct phenotypes—combined with either dermal- or lymph node-derived fibroblasts. We aimed to investigate how these cellular combinations influence MCTS formation, spatial architecture, and invasive behaviour. We hypothesised that the interplay between different cSCC and fibroblast cell combinations would differentially influence spheroid formation and invasion. Methods: Using live-cell microscopy we assessed the spatial architectures specific to each cell line-fibroblast combination and evaluated the expression of EMT and CAF markers. Furthermore, we utilised MCTS in invasion models to investigate associations between the mode of invasion and the EMT phenotype of the cancer cell line. Results: We show that metastatic cSCC/fibroblast MCTS self-organise into distinct spatial architectures. They also invade through collagen in a manner influenced by fibroblasts but dominated by the EMT status of the originating cancer cells. Conclusions: These findings highlight the physiological relevance and utility of MCTS as models for investigating tumour–stroma interactions and invasion dynamics in metastatic cSCC.