KIT and PDGFRA mutations and PDGFRA immunostaining in gastrointestinal stromal tumors

In the present study, we investigated the association of PDGFRA and KIT mutations as well as PDGFRA immunohistochemical expression with clinicopathologic features and prognosis in a series of gastrointestinal stromal tumors (GISTs). Tumor DNA from 40 GISTs was sequenced for the presence of mutations in KIT exons 9, 11, 13 and 17, and in PDGFRA exons 12 and 18. Tissue sections were stained with polyclonal anti-PDGFRA antibody. KIT mutations occurred in 26 cases. There were 13 deletions, 6 substitutions, 3 deletion-substitutions, 3 duplications and 1 insertion. Tumors with KIT deletions/insertion were large with a high mitotic index (MI), and were associated with a high rate of symptoms at diagnosis, invasion into adjacent organs, distant metastasis, relapse and a short disease-free survival (DFS). PDGFRA mutations occurred in 6 gastric GISTs. There were 4 deletions and 2 substitutions. Tumors with PDGFRA mutations were small, with a low MI and Ki67 score, and were associated with a very low rate of symptoms at diagnosis, invasion into adjacent organs and distant metastasis. PDGFRA immunopositivity was found in 23 cases: a peculiar ‘dotlike’ staining was found in 5 out of 6 PDGFRA mutated cases. Patients with positive PDGFRA immunostaining had a longer DFS than those with negative staining. Our data confirm that the type of KIT mutation is associated with various clinicopathologic features of GISTs, and indicate that PDGFRA mutations are associated with rather indolent tumors. PDGFRA immunopositivity reflects PDGFRA mutational status and is associated with a favorable outcome.