The majority of gastrointestinal stromal tumor (GIST) are driven by mutations in KIT or platelet derived growth factor receptor alpha (PDGFRA) receptor tyrosine kinases. Imatinib, a type II KIT/PDGFRA tyrosine kinase inhibitor (TKI), is the first-line treatment for advanced GIST. However, the most common PDGFRA mutation, exon 18 D842V, is strongly resistant to imatinib and other type II TKIs. Over 80% of unique PDGFRA mutations in GIST occur in exon 18, and they include many complexities such as in/dels and additional point mutations. It is largely unknown how these mutations respond to imatinib, but many are assumed to be resistant, like D842V. Contrary to these assumptions, we have shown in our in vitro models that some of these clinically observed exon 18 mutations were imatinib sensitive. Imatinib sensitivity also seemed to be dependent on the characteristics of the amino acid at the 842 position, which led us to hypothesize that sensitivity is largely determined by this residue. To test this hypothesis, we cloned and expressed every possible variant at the 842 position in Ba/F3 cells and determined imatinib sensitivity via immunoblotting.