Somatostatin receptor expression in metastatic NET lesions depends on primary tumor site

Objectives In patients with neuroendocrine tumors (NET) 68Ga-DOTA-Tyr-octreotide (DOTATOC)-PET/CT is a tool of growing importance for tumor-detection, therapy planning and control. Even though the somatostatin receptor expression can be relatively quantified using standard uptake values (SUV), just few trials have so far aimed to determine characteristic ranges for SUV in primary and metastatic NET-lesions of specific localisations. We present a descriptive analysis of SUV ranges in NET and their metastases.

Methods Ga68-DOTATOC-PET/CT-Scans of 80 Patients with metastasised NET of the small bowel (38%), pancreas (20%), lung (11%) or other/unknown primary (31%) were analysed retrospectively. SUVmax in metastatic lesions was compared to SUVmax of the primary tumor site. We furthermore correlated SUVmax of the primary tumor lesions to SUVmax in the organ-specific metastatic lesions.

Results SUVmax of metastatic lesions was significantly higher in pancreatic NET (20.9; n=11) than in NET of the small bowel (16.7; n=54). Mean SUVmax in liver-metastasis was 20.5 (SD 19.1; range 5.1 - 64.4) and 18.7 (SD 18.1; range 3.2 - 59.9) in the corresponding primary tumor site. In lymph node metastases we observed a mean SUVmax of 13.0 (SD 10.2; range 1.9 - 28.1) and 14.3 (SD 6.8; range 6 - 25.4) in the corresponding primary tumor site. A significant correlation between SUVmax in organ-specific metastases and in primary NET was found in patients with liver-metastases and in lymph node metastases.

Conclusions In this retrospective study metastatic NET lesions showed higher SUV values in pancreatic NET than in bowel NET with the SUV in metastatic lesions closely correlated to the primary tumor SUV. Since SUV values represent the somatostatin receptor expression on NET-cells, these findings might be used in the future for response prediction of radiopeptide therapy in metastasised NET. Further prospective studies should be carried out to confirm our findings