A fusion protein is a protein composed of several domains (parts) that are encoded by separate genes and have been joined so that they are transcribed and translated as a single unit, producing a single polypeptide maintaining functional properties of each original protein. Fusion proteins can be created “in vivo” and “in vitro” by using recombinant DNA techniques for use in biological research or therapeutics. Fusion proteins occur naturally and commonly in cancer cells, where they may function as oncoproteins having different functions or physico-chemical patterns.