[72] Gastrointestinal Stromal Tumors (GISTs) of the Omentum A Cllinicopathologic Study of 95 Cases

M Miettinen, LH Sobin, J Lasota. Armed Forces Institute of Pathology, Washington, DC

Background: GISTs, KIT-positive and oncogenetic KIT/PDGFRA mutation-driven mesenchymal neoplasms, most commonly originate from the stomach or small intestine, but a small number of GIST is believed to primarily involve the omentum. Mutation status, histology, and long-term prognosis of omental GISTs are poorly understood.
Design: We analyzed 95 GISTs that were surgically designated as omental tumors. Immunohistochemical studies were performed to evaluate KIT, CD34, and SMA expression. KIT and PDGFRA mutations were analyzed on 37 cases following PCR amplification and direct sequencing. Histologic features, tumor size, single vs. multiple tumors, and follow-up status were analyzed.
Results: There were 46 females and 49 males of ages 48-88 yrs (median, 60 yrs). KIT mutations were detected in 15 cases (12 in exon 11 with 7 deletions, 4 substitutions, 1 duplication; 3 exon 9 duplicaztions). PDGFRA mutations were detected in 11 cases (9 in exon 18, 2 in exon 12), and wild-type for both genes in 11 cases. The tumors were single in 52 cases, multiple in 38 cases, and indeterminate in 5 cases. The two first groups were analyzed for selected factors. Single tumor cases showed the following: KIT+ 40/43, CD34+ 21/35, SMA+ 12/38, mitoses median 3/50 HPFs, tumor size median 14 cm, median survival of 120 months (range, 0-397 months). 39 tumors had histological features typical of gastric GISTs, and 13 of small intestinal GISTs. Ten of the single tumors were attached to stomach, and 5 of these patients were alive at the end of follow-up (median survival time for living patients, 235 months). Multiple tumor cases showed: KIT+ 22/23, CD34+ 7/20, SMA+ 3/21, mitoses median 11/50, tumor size median 17 cm, median survival 8 months (all died). 20 tumors had histologic features of small intestinal and 18 of gastric GISTs.
Conclusions: Omental GISTs are a heterogeneous group. A majority of tumors presenting as single tumors have features of gastric GISTs, and high frequency of PDGFRA mutants support common gastric origin for these tumors. Omental GISTs include a small prognostically favorable subgroup: single GISTs attached to stomach of gastric origin forming a dominant omental mass. Also, patients with low mitotic rates have a longer survival. Multiple tumor presentation has a poor prognosis, and GISTs with features of small intestinal ones cluster in this group. All omental GISTs probably primarily originate from the GI tract.
Category: Bone & Soft Tissue

Monday, March 9, 2009 1:00 PM

Poster Session II # 24, Monday Afternoon