Invasion and invasive can refer to a procedure that 
requires an instrument or device to be inserted into the 
body through the skin or through a body opening for 
diagnosis or treatment. An example would be a needle 
being inserted into a vein (a blood vessel that carries 
blood to the heart). These terms can also mean the 
beginning of a disease. Invasion also means the act of 
spreading, entering, or intruding into, through, or 
throughout something (such as healthy tissue). One 
example would be a knife wound or gunshot wound. 
 
An invasion can slowly or rapidly filter into or through something else. Another example of 
an invasion is the spreading, entrance, intrusion, or reproduction of microorganisms (tiny, 
living organisms) into the body. 
Yet another example is the local spread of a harmful growth of new cells or tissues that  
serves no healthy function for the body (such as cancer). Cancer is a group of diseases  
characterized by an abnormal and excessive growth of cells in one of the body organs or 
tissues.
Invasion and invasive are also used to describe the process by which harmful cells move 
through the basement membrane and gain access to blood vessels and lymphatic 
channels. 
 
The basement membrane is a thin sheet of fibers that form the bottom 
of the epithelium. Epithelium is a group of cells that occur in one or more 
layers, which cover the entire surface of the body and line most of the 
hollow structures in it. Lymphatic channels are passageways that lymph 
goes through. Lymph is a milky fluid that contains proteins, fats, and 
term "invasion" is used to describe a growth of new cells or tissue in the 
epithelium that serves no healthy function for the human body, it means 
that the new tissue has spread to the bottom layer of the epithelium. 
The opposite of invasive is non-invasive. Invasion and invasive come  
from the Latin word "in" meaning "within," and the Latin word "vadere" 
meaning "to go." Put the two words together and you have "to go 
within."