The stromal tumors of the gastrointestinal area usually show a mutation in the KIT-tyrosine kinase. This is a membrane protein, acting as a receptor and controlling cell proliferation among other functions. The mutated KIT-tyrosine kinase is uncoupled from the regular biological regulatory processes and is constitutively active. KIT is traceable via the CD117 antigen, e.g. through the ELISA technique.