Figure 2.

Tumor architecture. A) A solid tumor is composed of malignant parenchyma and benign tumor stroma that supports tumor growth and structure. There are diverse types of stromal cells including cancer-associated fibroblasts, immune cells, and other cells forming the cellular part of tumor stroma. The noncellular parts of the tumor stroma including extracellular matrix and cytokines surround and interact with the embedded cells. An abnormal vascular network is always observed in a solid tumor, which is essential for tumor supply. In addition, low pH, hypoxia, and high interstitial pressure are charateristics of solid tumors. All these tumor components interplay to form a complex microenvironment and drive the tumor development. B) The tumor vasculature is highly abnormal and at least six types of blood vessels with different characteristics have been distinguished.