P1745 - Perirectal Extragastrointestinal Stromal Tumor Biopsied With Endoscopic Ultrasound-Guided Fine Needle Aspiration

Mohamed M. Elagami, MD, Alman Khalid, MD, Vinod Kumar, MD, Monisha Singhal, MD, Youssef Botros, MD, Matthew Grossman, MD, Gabriel Melki, MD, Walid Baddoura, MD, Michael Maroules, MD
St. Joseph's University Medical Center, Paterson, NJ

Introduction: GISTs account for up to 3% of all GI tumors. They are known for their wide variability in biologic behavior and malignant potential. When GISTs occur outside of the GI tract, they are termed Extra-gastrointestinal stromal tumors [EGISTs] and they maintain the histopathological and molecular characteristics of GISTs. Most GISTs arise from the stomach (70%) and small intestine (30%). A small percentage also occur in the large intestine (5%) and esophagus (5%). Malignant potential is evaluated using several parameters which include size, location, invasion of adjacent organs, mucosal invasion.

Case Description/Methods: A 41-year-old Algerian male who presented with RLQ abdominal pain for 2 weeks with no other GI or GU symptoms. MRI showed a 7 cm mass abutting the sigmoid colon but did not arise from the wall of the large intestine and was highly suspicious for a neoplasm [Figure 1]. After a multidisciplinary discussion the decision was made to obtain an endoscopic ultrasound (EUS) and biopsy of the mass. This study showed a heterogenous mass in the anterior perirectal space with some lymph node involvement without any invasion in the rectum or urinary bladder. Using a transrectal approach, a FNA with 19 Gauge biopsy needle was performed. Results showed proliferation of spindle cells, with focal prominent cytoplasmic perinuclear vacuoles and focal marked nuclear atypia and infrequent mitotic activities. The mass had a size of 7 centimeters (single largest dimension), mitosis rate of 5 out of 50 high power fields (HPF) and a 25% risk for metastasis. Using the National Institute of Health Fletcher criteria for GIST risk assessment we determined that this is a high-risk tumor (Table 1).

Discussion: The one-year and five-year survival rate for EGIST is 91.7% and 48.9%, respectively. According to the NCCN, the workup for GIST/EGIST should include a thorough H&P, CBC, LFT, CT abdomen and pelvis with contrast or MRI, and surgical assessment. An endoscopic transmural biopsy can be considered if the risk of peritoneal seeding by the tumor is low. Otherwise, percutaneous transperitoneal biopsy is more appropriate. Morphologic diagnosis based on microscopic examination of histological sections is the standard for GIST diagnosis. The NCCN recommends the use of imatinib 400mg in advanced or metastatic GIST or increasing the dose to 800mg if exon 9 KIT mutation is positive. Surgery is the only potential cure for GIST and is aimed at resecting the tumor with histologically negative margins.




Disclosures:


Mohamed M. Elagami, MD, Alman Khalid, MD, Vinod Kumar, MD, Monisha Singhal, MD, Youssef Botros, MD, Matthew Grossman, MD, Gabriel Melki, MD, Walid Baddoura, MD, Michael Maroules, MD. P1745 - Perirectal Extragastrointestinal Stromal Tumor Biopsied With Endoscopic Ultrasound-Guided Fine Needle Aspiration, ACG 2021 Annual Scientific Meeting Abstracts. Las Vegas, Nevada: American College of Gastroenterology.