Detection of Somatostatin Receptors by Ligand Derivative Staining in Breast Tumors

Somatostatin receptors (SSTRs) are G protein-coupled receptors that inhibit tumor cell proliferation. SSTRs are also expressed in breast cancer cells, and examination of clinical breast cancer specimens has revealed that SSTRs are more prevalent in patients with lower malignancy rates. However, in clinical trials of breast cancer, no significant differences in survival rates were detected upon administration of somatostatin analogs, highlighting the importance of detecting SSTRs in tumor tissues. Herein, we determined the expression of SSTRs in breast tumors using immunohistochemistry and ligand derivative staining (LDS) and examined the relevance of SSTR expression. Pathological tissues from breast tumors diagnosed as invasive ductal carcinomas (n=85) or breast neuroendocrine tumors (NETs) (n=20) were used. Immunohistochemistry and LDS using fluorescein isothiocyanate (FITC)-labeled octreotide were performed to detect SSTR expression. Immunohistochemistry of SSTR2 in breast cancer tissues revealed a significant positive association with estrogen receptor (ER) (p<0.001) status, a significant negative association with stage (p=0.023), and a negative association with pN (p=0.055), which did not reach statistical significance. LDS in breast cancer demonstrated a significant positive association (p=0.027) with SSTR2 immunohistochemistry, a positive tendency with ER (p=0.065), and a negative association with pN (p=0.061). LDS in breast NETs was not associated with SSTR2 expression. Our findings revealed that immunohistochemistry allows specific detection of SSTR isoforms, whereas LDS could comprehensively evaluate SSTR expression. To the best of our knowledge, this is the first study to detect SSTR expression in breast cancer tissues using LDS, and the results suggest LDS as a new mode of evaluating SSTR status in clinical specimens.