An unusual submucosal lesion

We report the case of a 33y old woman who underwent upper-GI endoscopy for epigastric pain. The first endoscopy showed a pericentimetric submucosal lesion located on the lesser curve of the antrum. The superficial biopsies of the lesion concluded to chronic gastritis. An echo-endoscopy was performed to obtain new biopsies, and showed a well-defined, hypo-echoic, submucosal lesion of approximately 16mm. Biopsy was not possible because of its mobility. At this point, the differential diagnosis were leiomyoma and GIST. To obtain a formal diagnosis through mucosal incision assisted biopsy, a second endoscopy was performed 4 months later; the lesion had significantly grown (to 25mm), presenting as a Paris 0-Ip lesion, with superficial ulceration (figure 1). What is your diagnosis?