MDK and neoplasm: As a result, pericytes, which are predominant in metastasis tissues, were revealed to have broad interactions with B cells, cytotoxic T cells, dendritic cells, endothelial cells, epithelial cells, M1 macrophage, memory T cells, regulatory T cells, monocytes, and NK cells via the MDK-NCL pathways, which is an important hallmark in the change of tumor microenvironment, and serves as a sign of cancer-associated fibroblasts (CAF) activation to stimulate downstream pathways for facilitating tumor invasion [42].