Extra-gastrointestinal stromal tumors (eGISTs): Experience of a cooperative group.

Abstract

10558 Background: eGIST occurs in regions such as omentum, mesentery, retroperitoneum and undefined abdominal and pelvis locations. Some authors hypothesized that the origin are Cajal interstitial cells from the abdominal cavity or the tumors are mural GISTs with extramural growth. Clinical, pathology and molecular profile of eGIST is similar to GISTs. Some publications show higher size and mitotic index than GIST. eGISTs are not consider in risk stratification consensus. Differential diagnosis of abdominal or pelvis mass with other tumors requires expert pathologist. The aim of the study is to evaluate clinical characteristics and mutation profile of consecutive eGISTs from a prospective database. Methods: Data from patients (pts) with histologic diagnosis of GIST with no evidence of gastric or intestinal involvement was analyzed. Demographics and medical information was obtained from an Argentinean GIST prospective database. Mutation analysis was performed with HPLCA. Descriptive statistical analysis was used. Results: Between 2004 and December 2013, 63 pts with eGISTs were included. Median age was 56 years old (16-87). Thirty three (52%) pts were female. Primary sites were: retroperitoneum 13 pts (21%), mesentery and omentum, 22 pts (35%), pelvis 17 (27%), peritoneum 9 pts, thoracic wall and pleura in two pts. Complete surgical resection was performed in 14 pts (35%). Initial pathology report was other than eGIST in 19 pts (30%). Median size tumor was 8 cm (1-39) and 47% had >10 mitoses/50 HPF. Positive C-KIT was in all pts. Median time to recurrence in pts was 11 months (1-12). Liver was the most frequent site of relapsed (9 pts). Exon 9,11,13, 17 KIT and 12, 14, 18 PDGFR mutations were evaluated in 24 pts. Exon 11 KIT deletion was the most frequent mutation (5 pts) and 12 (50%) were Wild type KIT and PDGFR. Imatinib was the systemic in 42 pts. Objective clinical benefit was 60%. Conclusions: eGISTs is a rare entity. In our series there was a female predominance located mostly in mesentery and omentum. Higher size and mitotic index was observed. One third of pts were complete resected and pathologic misdiagnosis. Better pre-operative approach should be required in this group of pts and more knowledge is necessary to improve outcome.