The  stroma in a malignant tumor, comprising  extracellular matrix and embedded cells, constitutes up to 90% of the tumor mass and has characteristics not found in normal tissues. In tumor stroma, tumor-associated cells such as carcinoma-associated fibroblasts, inflammatory cell, and endothelial cells among others are found to secrete soluble growth factors and cytokines as well as extracellular matrix molecules and extracellular matrix degrading enzymes that promote transformation and malignant progression of tumor cells. Cancer appears to be a product of the tumor-host  microenvironment, where mutual stimulation of tumor and stromal cells induces tumor formation and, extensive tumor  angiogenesis and  metastasis.