**2.5 Extravasation**

The escape of a tumor cell from the vessels is named as extravasation. Tumor cells invade from the interior of a vessel into the organ parenchyma. There is a debate in the literature about whether extravasation is necessary for metastases process. One key evidence for this dilemma originates from lung endothelium-attached tumor cells. The cells survive and grow intravascularly; therefore, further experiments are required to elucidate the molecular mechanism [1, 3].

### **2.6 Metastatic colonization**

Metastatic colonization is an inefficient metastatic cascade step in which progressively growing tumor forms at distant ectopic sites. This process involves the formation of new blood vessels to provide nutrients and oxygen. Micrometastasis contrast with colonization do not constantly grow but stays dormant for longer times. Metastatic colonization is the rate-limiting step of metastasis [3].
