A case of rectal gastrointestinal stromal tumor (GIST) preoperatively diagnosed by endoscopic ultrasound-guided fine needle aspiration (EUS-FNA)

Abstract

A 70-year-old woman, in whom a previously performed colonoscopy by another physician had revealed a submucosal tumor in the lower rectum. She was therefore referred to our hospital for further examination. No ulcer formation was observed in a subsequent colonoscopy, however, endoscopic ultrasonography (EUS) depicted the lesion as a 30-mm mass with a well-defined border that appeared to have originated from the fourth layer, and the internal echo was relatively uniformly hypoechoic. The lesion was visualized similarly as a submucosal tumor on abdominal CT and MRI and no apparent distant metastases were observed. EUS-FNA was performed to obtain a definitive diagnosis. A 19G needle was used for the FNA. Cytological examination of the aspirated tissue revealed fusiform tumor cells. Positive immunostaining results were obtained for c-kit, CD34 and DOG-1. Ki-67 positivity rate was 9%. The mitotic figure count was over 14 per 50 high-power fields. On the basis of the above findings, the lesion was diagnosed as a high-risk GIST, and a laparoscopy-assisted low anterior resection was performed. The patient is currently under follow-up at our hospital on an outpatient basis. The risk categories for GIST are based on the tumor diameter and mitotic figure count. In this case, we were able to identify the lesion as high risk on the basis of the mitotic figure count in EUS-FNA. This method was useful for determining the course of treatment. We describe this case along with a brief review of the literature.