SSTR2a as a Prognostic and Therapeutic Biomarker for Prostate Cancer: An Immunohistochemical and RT-PCR Analysis
XY Tang, S Takekoshi, S Umemura, RY Osamura. Tokai University, Isehara, Kanagawa, Japan
Background: In human prostate cancers, although hormonal therapy has been useful and sensitive for androgen receptor (AR) positive cases, therapy is very limited for AR-negative, advanced or recurrent cases. Somatostatin analogues have been used as therapeutic agents in somatostatin receptor type 2a (SSTR2a) positive cancers. It has been confirmed that they can inhibit the growth and metastasis in androgen-independent prostate cancers in vitro. The purpose of this study is to detect SSTR2a in human prostatic cancers by immunohistochemistry in order to predict the response to a new therapeutic method in advanced prostate cancer.
Design: Formalin-fixed and paraffin-embedded sections from 108 prostate cancer cases (97 radical prostatectomy cases and 7 of their metastatic lymph nodes, and 11 needle biopsy cases), were analyzed. The immunohistochemical study was performed by the Envision method using SSTR2a antibody (Gramsch Laboratories). Cases were considered positive if they were positive on the cell membrane or luminal surface. RT-PCR analysis was performed on 11 needle biopsy and 3 metastatic cases, after selection of appropriate carcinoma cells by laser microdissection.
Results: The study showed expression of SSTR2a in 13 of the 108 cases (12%); The histological grade (Gleason) and tumor stage of the prostate cancer were directly related to SSTR2a expression (u-test, p=0.013 & p=0.0014, respectively); Among the seven cases with lymph node metastasis, SSTR2 expression was markedly higher in frequency than in the 101 non-metastatic cases (u-test, p=0.0096); SSTR2 mRNA was detected in only 4 of 11 cases by needle biopsy and 1 of 3 cases of LN metastasis by RT-PCR. Although not statistically significant, the metastatic carcinoma cells revealed higher mRNA levels than primary prostate carcinoma cells. Interestingly, in SSTR2a positive cases, SSTR2a-expression was only identified in some of the carcinoma cells. The results indicate that the SSTR2a positive carcinoma cells probably have a stronger tendency for metastasis, and this phenomenon may be applicable to androgen-independent metastatic or recurrent cases.
Conclusions: SSTR2a is a prognostic factor of metastatic potential in prostatic carcinoma. Somatostatin analogues may be beneficial for patients with advanced prostate cancer if they are positive for SSTR2a.
Category: Genitourinary (including renal tumors)
Wednesday, March 11, 2009 1:00 PM
Poster Session VI # 114, Wednesday Afternoon