A case of small pancreatic neuroendocrine tumor of less than 10 mm showing metastasis to multiple organs.

Small non-functioning pancreatic neuroendocrine tumors (pNETs) measuring under 10 mm are considered eligible for observation and follow-up, although a minority of small NETs may exhibit show an aggressive behavior. We report a case of small G2-NET that was surgically removed and later developed metastatic recurrence in multiple organs. The patient, a woman in her sixties with a pancreatic body cyst, had been under follow-up for more than a decade. Several years later, a hypoechoic area appeared in the pancreatic body. Endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) was performed twice; however, a definitive diagnosis was not obtained. Subsequent EUS revealed extension of the lesion into the main pancreatic duct, which was diagnosed as a pancreatic body tumor with intraductal extension. Distal pancreatectomy was performed, and histology revealed a small G2-NET, measuring 8 × 7 mm in diameter. Multiple metastatic tumors were detected 4.5 years after surgery, and the patient is currently undergoing treatment with everolimus and lanreotide. This case supports the viewpoint that small G2-NETs, even those measuring less than 10 mm, may have a risk of metastasis, highlighting the need for careful follow-up and appropriate therapeutic interventions.