Quantitative Evaluation of Somatostatin Receptor Subtype 2 Expression in Sporadic Colorectal Tumor and in the Corresponding Normal Mucosa

Purpose : The somatostatin (SS) receptor subtype 2 (sst2) is the principal mediator of the antiproliferative effects of SS and has the highest affinity for the commercially available SS analogues. The purpose of this study was to evaluate sst2 mRNA expression by quantitative reverse transcription-PCR (RT-PCR) in colon cancers and in corresponding normal tissues. Experimental Design : The expression of sst2 mRNA was measured with a quantitative method based on real time RT-PCR with TaqMan assay in 100 colon cancers and in the corresponding normal tissues. In a limited number of patients, these results were compared with those obtained by in situ hybridization ( n = 26) and by in vivo imaging with 111 In-pentetreotide ( n = 17). Results : Results obtained by quantitative RT-PCR on sst2 expression in colorectal cancer were significantly related to those obtained by in situ hybridization and 111 In-pentetreotide scintigraphy. Sst2 was expressed in all of the tumors investigated without any relationship with localization, grading, and stage of disease. Although the paired, unaffected mucosa tends to express a higher abundance of sst2 than the corresponding cancer samples, this difference did not reach a statistical significance. However, in patients with elevated carcinoembryonic antigen levels (>5 ng/ml) there was a significant loss of sst2 mRNA in the tumor when compared with its paired normal tissue. Conclusions: In this study we confirmed, by a quantitative method, that colorectal cancer does not express higher concentrations of sst2 mRNA than the corresponding unaffected tissue. Conversely, a loss of sst2 was found in patients with elevated preoperative concentrations of carcinoembryonic antigen, an unfavorable prognostic marker for colorectal cancer.