SAT-078 - When Bloating Signals More: Neuroendocrine Tumor of Unknown Primary

Introduction
Neuroendocrine neoplasms (NENs) are rare tumors that originate from widely distributed cells within the neuroendocrine system. NENs can occur within almost any organ, and their most common site is the gastrointestinal tract (>60%). The lung is the second most primary common site (>20%). However, neuroendocrine with unknown primary site may occur, accounting for 10 to 14 percent of all NENs
This is a case highlighting a rare NENs with an unknown origin.

Case
This is a 32-year-old male with no significant medical history who presented with abdominal bloating and nausea. He had recently returned from a holiday in Mexico during which he notably had engaged in social binge drinking. No previous history of tobacco use. He drinks alcohol socially.
Only abnormalities in lab findings included leukocytosis and transaminitis. An abdominal ultrasound and MRI of the abdomen and pelvis revealed hypo vascular masses compatible with metastasis and prominent likely metastatic lymph nodes in the left upper quadrant adjacent to the left adrenal gland.A Chest CT ruled out any obvious lung mass. Given that colon cancer is a common source of liver metastasis, a colonoscopy was performed to evaluate for a primary source. The procedure did not reveal any colon cancer.
Due to concerns of metastatic carcinoma,a liver biopsy was performed. This subsequently revealed a high-grade neuroendocrine tumor.
The patient was started on etoposide and transferred to a tertiary institution for further management.

Discussion
This patient’s NEN presented as a benign symptom of bloating, which contributed to the diagnostic challenge and increased likelihood of being overlooked. Most neuroendocrine tumors (NET) are of gastrointestinal (GI) origin. However, this patient's extensive diagnostic evaluation including colonoscopy, CT abdomen and MRI abdomen and pelvis did not reveal a GI source. His CT chest did not reveal any mass either. Hence this patient’s metastatic neuroendocrine carcinoma can be categorized as NET of unknown origin.
Typically, the primary tumor location can be gleaned from the patient’s symptoms, however this patient primarily endorsed nonspecific symptoms of bloating and nausea for two months, followed by minor RUQ pain and vomiting for one week. Due to the patient’s age and nonspecific symptoms, it is likely that the patient experienced diagnostic delay due to low clinical suspicion.

Conclusion
Neuroendocrine tumors of unknown primary (NET-UP) are very rare, attributing to less than 5% of all cancers with unknown primary sites. Patients with NET-UP typically have very poor prognosis compared to those with known primary site, making early diagnosis and grading essential for guiding the treatment plan. This case underlines the importance of considering NET in the differential of cancer with liver metastasis, regardless of the patient's symptoms.

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