Significance of Cancer-Associated Fibroblasts in the Interactions of Cancer Cells with the Tumor Microenvironment of Heterogeneous Tumor Tissue

SIMPLE SUMMARY: The tumor microenvironment (TME) is composed of various cell types and extracellular components and plays an important role in cancer development and progression, as well as in therapeutic resistance and metastasis. Cancer-associated fibroblasts (CAFs) are a key cell type in the TME and interact with cancer cells as well as with other TME cells, such as immune cells. Immunocompetent mouse cancer models that recapitulate the interactions of cancer cells with the TME have provided a better understanding of the TME network and support the development of new therapeutic strategies. In this review, we focus on cancer cell–TME interactions in heterogeneous tumor tissue, and we provide an overview of therapeutic strategies that target the TME. ABSTRACT: The tumor microenvironment (TME) plays a key role in cancer development and progression, as well as contributes to the therapeutic resistance and metastasis of cancer cells. The TME is heterogeneous and consists of multiple cell types, including cancer-associated fibroblasts (CAFs), endothelial cells, and immune cells, as well as various extracellular components. Recent studies have revealed cross talk between cancer cells and CAFs as well as between CAFs and other TME cells, including immune cells. Signaling by transforming growth factor-β, derived from CAFs, has recently been shown to induce remodeling of tumor tissue, including the promotion of angiogenesis and immune cell recruitment. Immunocompetent mouse cancer models that recapitulate interactions of cancer cells with the TME have provided insight into the TME network and support the development of new anticancer therapeutic strategies. Recent studies based on such models have revealed that the antitumor action of molecularly targeted agents is mediated in part by effects on the tumor immune environment. In this review, we focus on cancer cell–TME interactions in heterogeneous tumor tissue, and we provide an overview of the basis for anticancer therapeutic strategies that target the TME, including immunotherapy.