Analysis of KIT mutation and protein expression in fine needle aspirates of gastrointestinal stromal/smooth muscle tumors

OBJECTIVE: To determine if sequencing the KIT gene could facilitate more de finitive FNA diagnosis. STUDY DESIGN: Sixteen cases of gastrointestinal stromal/smooth muscle tumor (GIST) in which fine needle aspiration (FNA) was performed (mean age, 67; M/F=12/4) were studied. DNA was extracted from cytologic preparations from all patients (15 cell blacks, I alcohol-fixed smear) and seven subsequent r esection specimens. DNA was amplified by polymerase chain reaction, using p rimers designed to amplify a segment of the KIT gene exon II and sequenced on an ABI Prism 377 DNA sequence analyzer (Applied Biosystems, Indianapolis , Indiana, U.S.A.). Immunocytochemical staining for CD 117 (the KIT gene pr oduct) was performed on sections from 12 cell blocks and 7 surgical resecti ons. RESULTS: In-frame deletion of exon II was detected in eight cases (7 monoal leic, 1 bialleic); a point mutation was found in one case. Mutation was fou nd only in histologically malignant (6 of 10 cases) and borderline GISTs (3 of 4 cases). No mutation was identified in benign tumors. In three cases, scant cellularity or blood precluded sequencing. CD 117 was expressed in 12 of15 cases. CONCLUSION: Immunocytochemical staining for CD 117 is useful in confirming a cytologic diagnosis of CIST but does not facilitate diagnosis of malignan cy. FNA biopsy specimens are suitable for KIT gene sequencing; detection of a KIT mutation favors a malignant diagnosis, though absence of mutation do es not preclude malignancy.