Quantification of immunohistochemical expression of somatostatin receptors in neuroendocrine tumors using 68Ga-DOTATATE PET/CT

The immunohistochemical expression of somatostatin receptor (SSTR) subtype 2 was compared to quantitative 68Ga-DOTATATE PET in neuroendocrine tumors (NET). In 27 patients suffering from metastatic NET the expression of somatostatin receptors (SSTR, score 0-3) and the Ki-67 index were assessed. The immunohistochemical findings were compared with the 68Ga-DOTATATE PET uptake in these tumors using the SUVmax (standardized uptake value). Both values were compared with the Ki-67 proliferation index. The SUVmax in NET without SSTR expression was significantly lower compared to those with SSTR expression (p <0.05), even though 3 out of 5 NETs with a score of 0 showed a high uptake of 68Ga-DOTATATE. The SUVmax correlated significantly (r=0.40, p <0.05) with the score of immunohistochemical SSTR expression (negative, score 0, moderate, score 1 and high, scores 2 and 3). The Ki-67 index correlated inversely with the SSTR expression score (r=-0.42, p <0.05), but not significantly with the SUVmax (r=-0.33, p=0.11). 68Ga-DOTATATE uptake was moderately correlated with the results of immunohistochemical SSTR analyses. However, SSTR negative NET may show high uptake of 68Ga-DOTATATE. (orig.)