1. ¹Department of Soft Tissue Pathology, Armed Forces Institute of Pathology, Washington, DC, USA
2. ²Department of Pathology and Division of Hematology and Oncology, Oregon Health & Science University Cancer Institute, Portland, OR, USA
3. ³VA Medical Center, Oregon Health & Science University, Portland, OR, USA
4. ⁴Department of Human Genetics, Catholic University of Leuven, Leuven, Belgium
5. ⁵Department of Pathology, University of Bonn Medical Center, Bonn, Germany
6. ⁶Department of Pathology, Hospital Northern Norway, Tromsø, Norway
7. ⁷Department of Pathology, Jagiellonian University, Krakow, Poland
8. ⁸Department of Biology and Genetics, Medical University of Gdansk, Gdansk, Poland
9. ⁹Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
10. ¹⁰Department of Pathology, Medical Faculty Hospital, Charles University, Plzen, Czech Republic
11. ¹¹Department of Oncology, Hospital Universitario de Son Dureta, Palma de Mallorca, Spain
12. ¹²Instituto Catalana de Oncologia, Hospital Clinic Barcelona, Barcelona, Spain

Correspondence: Dr J Lasota, MD, Department of Soft Tissue Pathology, Armed Forces Insitute of Pathology, 6825 16th Street, N.W., Building 54, Washington, DC 20306-6000, USA. E-mail: lasota@afip.osd.mil or jurek@erols.com

Received 31 May 2007; Accepted 18 June 2007; Published online 1 February 2008.

Abstract

Gastrointestinal stromal tumors (GISTs) are mesenchymal neoplasms driven by oncogenic, mutational activation of KIT or platelet-derived growth factor receptor (PDGFRA). GIST-specific KIT or PDGFRA mutations have been linked to tumor location, tumor cell morphology and clinical behavior. The purpose of this study was to evaluate the clinicopathologic profile of GISTs that have KIT exon 13 or exon 17 mutations. Through the collaboration of several GIST research groups, we gathered 54 cases from the pre-imatinib era that had such primary mutations. From our observations and those in the literature, we estimate that the frequency of these mutations is no higher than 1–2%. Almost all (32 of 33, 97%) of the KIT exon 13 mutations were the 1945A>G substitution leading to Lys642Glu. A majority (15 of 21, 71.4%) of the KIT exon 17 mutations were the 2487T>A substitution leading to Asn822Lys. Demographic and clinicopathologic data were available for 26 and 14 KIT exon 13 and exon 17 mutant GISTs, respectively. Median age and male to female ratio were similar to ones reported in other GIST studies. Small intestinal tumors were two times more frequent than gastric ones among KIT exon 17 mutants. Also, intestinal tumors were slightly overrepresented among KIT exon 13 mutants when compared with population-based studies. The majority of KIT exon 13 or exon 17 mutants had a spindle-cell morphology and only a few had epithelioid features. Tumor size varied from 1.2 to 25 cm and average mitotic rates were 9.5 and 4.2 for KIT exon 13 and exon 17 mutants, respectively. Gastric KIT exon 13 mutant GISTs tend to be slightly larger and more aggressive than gastric GISTs in average, whereas the behavior of small intestinal GISTs with KIT exon 13 mutations does not differ from other small intestinal GISTs. The latter is also true for all KIT exon 17 mutant GISTs.