[A Case of Giant Exophytic Gastric GIST Presenting with the Torricelli-Bernoulli Sign during Regorafenib Treatment].

Following surgery for rectal cancer and resection of the liver metastases, a giant gastric GIST was detected in an 81-yearold man during follow-up. Imatinib and sunitinib were administered; however, the tumor was refractory. Follow-up CT scans obtained while receiving regorafenib as third-line therapy revealed an increase in tumor size, and the disease was assessed as progressive (PD). At that time, a Torricelli-Bernoulli (T-B) sign was observed, indicating communication between the tumor interior and the gastric lumen. Reports of perforation during regorafenib administration are scarce, and the mechanisms underlying these events have not been fully elucidated. Conventionally, the T-B sign indicates tumor necrosis or perforation associated with a therapeutic response to GIST treatment. However, in this case, it is believed that structural destruction of the gastric wall resulted from tumor enlargement owing to drug resistance, thereby leading to the presence of gas. Therefore, we report this case as this course of events was highly informative to our understanding of the process of GIST perforation.