The development of biotechnology drugs represents one of the great advances in medical therapy and it was observed an exponential growth in its use. The resource to these drugs in Oncology and Hematology is no exception and it soon became an essential element of an integrated and directed therapy strategy. The expiry of the first biotechnology drugs patents has opened the door for the development and marketing of biosimilars, which entry in the Portuguese market was recently approved. This article was built on the analysis of the available state-of-the-art information on biotechnology drugs, biosimilars and current legislation and it expresses the opinion of Oncology and Hematology experts about the substituition of biological drugs by biosimilars in clinical practice.