Primary, resectable gastrointestinal stromal tumors (GISTs) originating from stomach and small intestine as different prognostically subtypes of disease.

10559 Background: The stomach (G) and small bowel (SB) are the most common primary sites of GISTs. However, the prognostic criteria for these GIST subtypes are still debatable. The aim of the study was to analyze the factors influencing the disease-free survival (DFS) in subgroups of G-GIST and SB-GIST patients based on the large prospectively collected registry.,In group of 440 primary GISTs CD117(+) treated surgically (resection R0/R1) with curative intention we identified 208 G-GISTs (47%) and 168 SB-GISTs (38%) and in these subgroups we analyzed factors influencing on DFS (from date of radical surgery to date of relapse/last follow-up). Median follow-up was 33 months.,G-GISTs as compared with SB-GISTs were significantly smaller (median size: 5 and 9 cm, respectively; p<0.0001), with less mitotic activity (median: 3/50 vs. 5/50 HPF; p=0.01) and patients were older (median age: 62 vs 56 years; p=0.02). The most common mutations in G-GISTs were exon 11 KIT (56%) and exon 18 PDGFRA (18%), and in SB-GIST - exon 11 KIT (65%) and exon 9 KIT (14%). The prognosis of G-GISTs was significantly better than SB-GISTs (5-year DFS rate: 64% [SD±5%] vs. 31% [SD±5%], respectively; p<0.0001). In G-GIST group the following factors demonstrated negative impact on DFS in univariate analysis: primary tumor size >5 cm and >10 cm (p<0.0001), mitotic index >5/50 and >10/50 HPF (p<0.0001), male gender (p=0.01), resection R1/tumor rupture (p<0.01) and high or intermediate NIH risk group (p<0.0001). In SB-GISTs group the following factors demonstrated negative impact on DFS in univariate analysis: primary tumor size >5 cm (p<0.001), mitotic index >5/50 HPF (p<0.001), resection R1/tumor rupture (p<0.01), epithelioid-cell or mixed-cell pathologic subtype (p=0.01), and high or intermediate NIH risk group (p<0.0001). According to multivariate analysis in both groups primary tumor size and mitotic activity or NIH risk group (+additionally gender in G-GIST) demonstrated independent influence on DFS.,GISTs originating from small bowel have worse prognosis than primary tumors located in the stomach. In both groups primary tumor size and mitotic activity are the most important factors in relation to disease recurrences. [Table: see text].