About this Research Topic
The role of tumor microenvironment has been demonstrated for a long time during tumor progression. Tumor stroma develops and evolves as a result of multiple interactions between carcinoma and mesenchymal cells, involving a reactive extracellular-matrix mediating a complex signalization. The timing of disease progression is critical in predicting clinical outcome and treatment response.
During carcinoma progression, cancer-associated fibroblasts (CAF) promote cancer invasion, angiogenesis, metastasis and resistance to chemotherapy. Other cell types participate to these interactions including mesenchymal, inflammatory and endothelial cells. Some of them may be derived from the tumor itself, along a process called epithelial mesenchymal transition (EMT). During this process, partially dedifferentiated carcinoma epithelial cells loosen cell–cell adhesion structures. They modulate their polarity, cytoskeleton organization and typically express vimentin filaments and downregulate cytokeratins. They become motile, resistant to anoikis and, depending on the tumor type, may become difficult to distinguish from bona fide mesenchymal cells. EMT was originally defined in the context of developmental stages, including heart morphogenesis, mesoderm and neural crest formation. The relevance of the EMT concept in carcinoma environment is supported by in vitro and in vivo models using transformed epithelial cells. It is also reinforced by the raising interest in circulating tumor cells, typically resulting from an EMT process. Transduction pathways typical of embryogenic EMT in vivo were also found to be activated during cancer progression. They converge on the activation of several families of transcription factors including Snail, Twist and Zeb families. More recently, it has been found that these pathways determine an increased phenotypic plasticity linked to cellular stemness and tumor initiating potential. They are also linked to apoptosis resistance, following chemotherapy or radiotherapy. Finally, direct connection has been observed between EMT transcription factors and tumor recurrence.
However, EMT transcription factors are also expressed by stroma cells that do not result from an EMT process. Their «non-EMT» role in the stroma signalling pathways, although associated with invasion and production of matrix metalloproteinases, remains still unclear.
Current studies explore these new aspects, investigate the molecular mechanisms involved and estimate their relative clinical importance in defined tumor types and cell environment, focusing on the tumor resistance to classic (conventional) therapies. These studies expose the various local aspects of carcinoma progression, including transcriptional and epigenetic mechanisms as well as genomic instability. The dissection of signals belonging to the stroma can reveal new treatment targets.
The aim of this Research Topic is to address the most recent aspects in the field of cancer-stroma interactions, including EMT-linked mechanisms. Studies linking the complexity of the cancer microenvironment to potential therapeutic strategies as well as molecular and cellular approaches and models, mathematical modeling and human genome-wide analysis will represent valuable contributions, in vitro or in vivo in pair with hypotheses, perspectives, opinions, and reviews.
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