PDGFRA and gastrointestinal stromal tumor: However, sporadic GIST most commonly occurs in the stomach.[7] GIST associated with NF1 has an alternative molecular pathogenesis.[8,9] Unlike sporadic GIST, GIST associated with NF1 appears to respond less well to tyrosine kinase inhibitors due to a lack of mutation in the c-kit gene or PDGFRA gene.