[418] DOG1 Antibody Demonstrates Higher Sensitivity Than KIT for Gastrointestinal Stromal Tumors in Cytology Cell Blocks

DG Hwang, X Qian, JL Hornick. Brigham and Women's Hospital and Harvard Medical School, Boston, MA

Background: Gastrointestinal stromal tumors (GISTs) usually occur in the wall of the gastrointestinal tract and may be inaccessible to endoscopic mucosal biopsy. Initial tissue sampling is therefore often obtained by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). Accurate diagnosis is critical to guide neoadjuvant therapy and surgical approach. Although 95% of GISTs are positive for KIT by immunohistochemistry on surgical specimens, staining for KIT is sometimes focal, and the limited material in a cell block can misleadingly appear KIT-negative. Several recent studies have demonstrated the higher sensitivity of the antibody DOG1 in the diagnosis of GIST in surgical material. In this study, we compare KIT and DOG1 in the diagnosis of GIST in cytology specimens.
Design: In total, 52 FNA cases with cell blocks diagnosed as GIST were selected. Cases were included if (1) the diagnosis was confirmed on surgical material (41 cases), or (2) when no surgical material was available, the cell block was positive for KIT (7 cases), or (3) in KIT-negative cases, the cell block was morphologically typical of GIST and negative for SMA and desmin (4 cases). In addition, 44 FNA cases of other intraabdominal or retroperitoneal tumors in the differential diagnosis of GIST were examined.
Results:

Immunohistochemical Results for DOG1 and KIT in Cell Blocks

	Total	KIT+/DOG1+	KIT-/DOG1+	KIT+/DOG1-	KIT-/DOG1-
GIST	52	40 (77%)	12 (23%)	0	0
Leiomyosarcoma	25	0	1 (4%)	0	24 (96%)
Leiomyoma	8	0	0	0	8 (100%)
Schwannoma	7	0	0	0	7 (100%)
Solitary fibrous tumor	2	0	0	0	2 (100%)
Desmoid fibromatosis	1	0	0	0	1 (100%)
Endometrial stromal sarcoma	1	0	0	0	1 (100%)

DOG1 was positive in all 52 GIST FNA cases. All 23 GIST specimens obtained by percutaneous FNA were positive for KIT. In contrast, 12 out of 29 GISTs (41%) sampled by EUS-FNA were negative for KIT; 8 of these showed KIT positivity on the surgical excision, while 4 lacked corresponding surgical material.
Conclusions: This study demonstrates that DOG1 is a more sensitive marker for GIST than KIT on the limited material available in cell blocks, and its sensitivity does not depend on the method of performing the FNA. In contrast, KIT was markedly less sensitive in EUS-FNA samples than those obtained by percutaneous FNA. DOG1 is also highly specific, with only 1 out of 44 non-GIST cases showing weak focal staining.
Category: Cytopathology

Tuesday, March 23, 2010 9:00 AM

Platform Session: Section F, Tuesday Morning