Tumor microenvironment is composed of all the untransformed elements in the vicinity of
tumor, mainly including a large number of stromal cells and
extracellular matrix proteins, which play an active role in most solid
tumor initiation and progression.
Carcinoma-associated fibroblasts (CAFs), one of the most common stromal cell types in the tumor microenvironment, have been demonstrated to be involved in
tumor growth, invasion, and
metastasis. Therefore, they are becoming a promising target for anti-
cancer therapies. In this review, we firstly summarize the current understandings of CAFs' molecular biology, including the heterogeneous cellular origins and molecular markers, and then, we focus on reviewing their various
tumor-promoting phenotypes involved in complex mechanisms, which can be summarized to the CAF-conveyed paracrine signals in
tumor cells, cancer stem cells, and
metastasis-initiating
cancer cells, as well as the CAF-enhanced extrinsic
tumor-promoting processes including angiogenesis, extracellular matrix remodeling, and
tumor-related
inflammation; finally, we describe the available directions of CAF-based target
therapy and suggest research areas which need to be further explored so as to deepen the understanding of
tumor evolution and provide new therapeutic targets for
cancer treatment.