Prospects of targeting the gastrin releasing peptide receptor and somatostatin receptor 2 for nuclear imaging and therapy in metastatic breast cancer

Background The gastrin releasing peptide receptor (GRPR) and the somatostatin receptor 2 (SSTR2) are overexpressed on primary breast cancer (BC), making them ideal candidates for receptor- mediated nuclear imaging and therapy. The aim of this study was to determine whether these receptors are also suitable targets for metastatic BC. Methods mRNA expression of human BC samples were studied by in vitro autoradiography and associated with radioligand binding. Next, GRPR and SSTR2 mRNA levels of 60 paired primary BCs and metastases from different sites were measured by quantitative reverse transcriptase polymerase chain reaction. Receptor mRNA expression levels were associated with clinico-pathological factors and expression levels of primary tumors and corresponding metastases were compared. Results Binding of GRPR and SSTR radioligands to tumor tissue correlated significantly with receptor mRNA expression. High GRPR and SSTR2 mRNA levels were associated with estrogen receptor (ESR1)-positive tumors (p