Receptor tyrosine kinases (RTK)s are the high affinity cell surface receptors for many polypeptide growth factors, cytokines and hormones. Of the ninety unique tyrosine kinase genes idenitified in the human genome, 58 encode receptor tyrosine kinase proteins. Receptor tyrosine kinases have been shown to be not only key regulators of normal cellular processes but also to have a critical role in the development and progression of many types of cancer.

   Approximately 17 different RTK classes have been identified

RTK class II ( Insulin receptor family) RTK class I ( EGF receptor family ) RTK class II ( Insulin receptor family) RTK class III (PDGF receptor family) RTK class IV ( FGF receptor family) RTK class V ( VEGF receptor family) RTK class VI (HGF receptor family) RTK class VII ( TRK receptor family) RTK class VIII ( EPH receptor family) RTK class IX ( AXL receptor family) RTK class X ( LTK receptor family) RTK class XI ( TIE receptor family) RTK class XII ( ROR receptor family) RTK class XIII ( DDR receptor family) RTK class XIV ( RET receptor family) RTK class XV ( KLG receptor family) RTK class XVI ( RYK receptor family) RTK class XVII (MuSK receptor family)