Tumors are commonly understood to consist of two elements, tumor cells and tumor stroma, with their association being responsible for macroscopic and microscopic characteristics of the neoplasm. It took many years to switch the focus in research from analyzing tumor cells to analyzing the complex tumor tissue, which includes tumor cells and the stroma (fibroblasts, immune cells, endothelial cells, mesenchymal fibers, and extracellular matrix). However, this approach has offered new critical insights into cancer pathogenesis and, subsequently, has enabled the development of new therapies.

Tumor cells induce various stromal alterations, with local angiogenesis being a very common one. Conversely, the tumor stroma is involved both in regulating tumor cell growth by secreting growth factors and cytokines with paracrine interactions and in promoting tumor invasion and metastasis. Epithelial-mesenchymal transition and its reverse process (mesenchymal-epithelial transition) are very good examples of biunivocal tumor-stromal interactions, helping to explain certain peculiar aspects of some tumors and their metastases. Recently, numerous drugs have been developed against various molecular targets aimed towards both tumor cells and the stromal component, some of the most recent with very encouraging results in routine practice.

This special issue invites authors to submit original research articles and reviews that address the tumor-stromal interactions with a role in tumorigenesis and tumor progression from both angles, tumor-induced mesenchymal changes and stromal-induced tumor alterations.

Potential topics include but are not limited to the following:

• Microenvironmental changes in tumors favoring local invasion and/or metastatic dissemination
• Intercellular communication between tumor cells and local mesenchymal cells either favoring or protecting against tumor progression
• Omics platforms for investigating epithelial-mesenchymal transition in malignant tumors
• Role of matrix metalloproteinases in tumorigenesis and tumor progression
• Role of cancer associated fibroblasts in tumorigenesis and tumor progression
• Role of local immune response in tumorigenesis and tumor progression
• Mesenchymal molecular targets in oncology