Metastatic hormone-refractory prostatic adenocarcinoma expresses somatostatin receptors and is visualized in vivo by [111In]-labeled DTPA-D-[Phe1]-octreotide scintigraphy.

Thirty-one patients with metastatic hormone-refractory prostatic adenocarcinoma were investigated scintigraphically with the 111In-labeled somatostatin analogue [DTPA-D-Phe1]-octreotide (OctreoScan) and with 99mTc-labeled HDP. In vitro somatostatin receptor autoradiography was performed on biopsies obtained from eight patients with hormone-refractory prostatic adenocarcinoma. In 30 of 31 patients (94%), at least one metastasis was positive at OctreoScan scintigraphy. Of the 346 lesions detected with 99mTc-labeled HDP bone scintigraphy, 128 were visualized with the OctreoScan technique, thus accounting for a 37% detection rate. Two uptakes on OctreoScan could not be identified on bone scintigraphy and were, thus, assessed as false positive. The biopsies of the eight patients disclosed a low density of receptors, localized on the tumor cells, as demonstrated with receptor autoradiography. Two patients with untreated metastatic prostatic adenocarcinoma were investigated in vivo before the start of endocrine therapy. However, none of the lesions detected by bone scintigraphy in these patients could be visualized with the OctreoScan technique. Positron emission tomography using [11C] methionine showed a decreased uptake in a metastatic index lesion in a patient treated with octreotide. It is concluded that hormone-refractory prostatic adenocarcinoma expresses somatostain receptors both in vitro and in vivo. The results obtained form the basis for the development of a new tool for in vivo characterization and of a new treatment strategy in patients with hormone-refractory prostatic adenocarcinoma.