A Retrospective Study Comparing Computed Tomography (CT) and 68Ga - DOTATATE PET/CT in Small Bowel Carcinoid Tumors

2144 Background: Neuroendocrine tumors (NETs) are a rare type of neoplasm which arise from the nervous and endocrine system and are characterized by an overexpression of somatostatin receptors (SSTRs). Carcinoid tumors are a subset of NETs that are often found in the gastrointestinal tract, most commonly the small bowel. When found early, these tumors are usually asymptomatic and detected incidentally on an exam or procedure performed for a different reason. However, if the tumor metastasizes to the liver, the patient may experience carcinoid syndrome. Carcinoid syndrome is caused by the release of serotonin and other hormones by the tumor that can result in difficulty breathing, abdominal pain, a fast heart rate, and redness in the face and neck. Imaging carcinoid tumors has historically relied upon a combination of CT and 111In-pentetreotide scintigraphy, the latter of which exploits the tendency of carcinoid tumors to overexpress SSTRs. Recently, the FDA has approved the use of 68Ga - DOTATATE PET/CT in the evaluation of NETs, which also functions by binding to SSTRs, namely the SSTR2 subtype. Therefore, the purpose of this study was to evaluate the clinical impact of 68Ga - DOTATATE PET/CT compared to conventional imaging with CT in patients with small bowel carcinoid tumors. Methods: This IRB, HIPPA compliant, retrospective study included patients who underwent 68Ga - DOTATATE PET/CT and contrast enhanced CT for imaging of small bowel carcinoid tumors from November 2016 to July 2017. Any patient who had not had a CT within 3 months of the 68Ga - DOTATATE PET/CT and/or any under the age of 18 years old were excluded from this study. Imaging reports were searched for the presence or absence of metastatic disease in mesenteric, retroperitoneal, iliac chain and upper abdominal lymph nodes, peritoneum, liver, bone, and sites outside of the abdomen and pelvis. Metastatic patterns between 68Ga - DOTATATE PET/CT and CT were then compared. Results: Twenty-nine patients with a primary small bowel carcinoid tumor (mean age 59 ±8 years, range 35-76; 15 M and 14 F) who had both a CT and 68Ga - DOTATATE PET/CT imaging within 3 months were included in this study. Twenty of 29 (70%) patients had metastatic mesenteric adenopathy on 68Ga - DOTATATE versus 13/29 (44%) on CT. Eight of 29 (28%) patients had metastatic retroperitoneal lymph node adenopathy on 68Ga - DOTATATE versus 4/29 (14%) on CT. 68Ga - DOTATATE PET/CT demonstrated iliac chain lymph node metastases in 5/29 (17%) patients versus 2/29 (7%) on CT. Two of 29 (7%) patients had upper abdominal lymph nodes metastases on CT compared to 8/29 (28%) on 68Ga - DOTATATE PET/CT. Ten of 29 (35%) patients had peritoneal metastatic disease on 68Ga - DOTATATE versus 2/29 (7%) on CT. 68Ga - DOTATATE PET/CT demonstrated liver metastases in 18/29 (62%) patients versus 13/29 (45%) on CT. Six of 29 (21%) patients had bone metastasis on 68Ga - DOTATATE versus 2/29 (7%) on CT. 68Ga - DOTATATE PET/CT showed evidence of distant metastatic disease in 20/29 (70%) patients including distant lymph nodes, cardiac, and pleural lesions. Overall, metastatic disease was identified in 27/29 (93%) patients with 68Ga - DOTATATE PET/CT, compared with only 14/29 (48%) with CT. Conclusions: In patients with small bowel carcinoid tumors, 68Ga- DOTATATE PET/CT detected more metastases than contrast enhanced CT, resulting in a considerable clinical impact. The incidence of peritoneal metastatic disease is also higher than previously reported, and better diagnosed by68Ga- DOTATATE PET/CT than conventional CT.