Back to Annual Meeting Posters

Background: While gastrointestinal stromal tumors (GIST) commonly arise from a gastric or intestinal (INT) location, extraintestinal GIST (E-INT) have been described. This study addresses the clinical and prognostic differences in GIST arising from the stomach or intestinal tract as well as extraintestinal or unknown (UNK) locations.
Methods: A prospectively maintained single-institution database of patients with the diagnosis of GIST was reviewed. Demographics, pathologic factors and survival were analyzed using Pearson's chi-square test, Fishers exact test, or Kaplan Meier curves where applicable.
Results: From 1990-2011, 282 patients with pathologic confirmation of GIST were referred to our center. The majority were male (56%) and Caucasian (83%). Tumors were commonly of gastric (N=148, 52%) or INT (100, 35%) origin. Less commonly, GIST arose from an E-INT (22, 8%) or unknown (UNK, 12, 4%) location. Multivariate analysis stratified by tumor origin showed that age varied across groups, with E-INT GIST found in older patients (median age 69 vs. 65 years for gastric, 60 for INT, and 64 for UNK, p=0.03). Tumor size was also greater in the E-INT group: median size 13cm vs. 6.4cm in gastric, 7.6cm in INT, and 8.6cm in UNK, p=0.05. Gender, ethnicity, and tumor mitotic rate were similar across groups. Additionally, use of neoadjuvant or adjuvant therapy was similar across groups.
Ultimately, 84% of gastric GIST underwent surgical exploration vs. 93% INT, 82% E-INT, and 50% of UNK-primary GIST. Nearly 10% of gastric and INT GIST were unresectable at surgery, vs. 44% E-INT. GIST of E-INT location also had higher rates of margin-positive resections, versus those of gastric or INT origin (56% vs. 12% and 24%, respectively, P<0.0001). The median follow-up was 77 months. Unknown primary and E-INT GIST exhibited a worse median OS (42 and 38 months, respectively), while INT or gastric GIST had better median OS (86 and 79 months, respectively, P<0.05). Smaller tumor size, negative surgical margins, lower mitotic rate, and use of tyrosine kinase inhibitors all positively impacted OS. 35% of gastric GIST developed recurrent disease vs. 61% INT and E-INT, and 100% of UNK primary GIST. Only mitotic rate and mutational status affected DFS; univariate analysis demonstrated mitotic rate>10/50 high power fields and PDGFRA mutations were associated with worse DFS (P<0.05). However, disease free survival (DFS) did not differ according to tumor origin.
Conclusion:
Although GISTs are considered to have variable malignant potential, E-INT and UNK GIST are more likely to be unresectable at presentation and to develop disease recurrence. Extraintestinal and unknown primary GIST have a worse OS. This may be due to a significantly larger tumor size and advanced stage at presentation that may prohibit effective surgical resection.