OBJECTIVETo investigate the expression of phospho-platelet derived growth factor receptor alpha (P-PDGFR-alpha) in gastrointestinal stromal tumors (GIST) and extra-gastrointestinal stromal tumors (EGIST) and its clinical significance.

METHODSExpression of P-PDGFR-alpha in 28 samples of positive CD117 and 13 samples of negative CD117 was detected by Envision immunohistochemical staining. Direct PCR sequencing was used to investigate the mutation status of c-kit gene exons 9, 11, 13, 17 and PDGFR-alpha gene exons 12 and 18.

RESULTSThe positive rate of P-PDGFR-alpha expression in GISTs with negative CD117 was 69.2%, which was significantly higher than that in GISTs with positive CD117 (7.1%, P<0.05). The positive rates of P-PDGFR-alpha expression in epithelioid GISTs(27.3%) and mixed GIST(63.3%) were both significantly higher than that in fusiform GISTs (9%, P<0.05). The positive rate of CD117 expression in fusiform GISTs (53.6%)was significantly higher than that in epithelioid GISTs (7.1%) and mixed GISTs(39.3%, P<0.05). C-kit gene mutation was found in 19 GIST cases with positive CD117. C-kit gene mutation was found in 19 of 28 GIST patients with positive CD117, among them, mutation of exon 11 occurred in 15 cases and exon 13 in 4 cases. No C-kit gene mutation was seen in 13 GIST patients with negative CD117. PDGFR-alpha gene mutation was found in 4 of 11 GIST cases with positive P-PDGFR-alpha and all occurred in exon 18.

CONCLUSIONSExamination of P-PDGFR-alpha expression may provide reliable evidence for the further improvement of pathological diagnosis,pathological typing and treatment for GISTs with negative CD117. Phosphorylated protein induced by PDGFR-alpha mutation may be associated with the important alternative molecular mechanism and the biological behavior of GIST development.