[588] Immunohistochmical Detection of SSTR2a in Gastro-Entero-Pancreatic Neuroendocrine Tumors (GEPNET) and Response to Somatostatin Analogue (SA).

Robert Y Osamura, Hanako Hirabayashi, Midori Matsuda, Taro Itoh. IUHW Mita Hospital, Minato-ku, Tokyo, Japan

Background: It has been reported that somatostatin analogue(SA) is expected to be effective for the gastroentero-pancreatic neuroendocrine tumors(GEPNETs) when they express somatostatin recetor(SSTR)2a by immunohistochemistry(IHC). This study is aimed at to elucidate the incidence of SSTR2a-positive GEPNETs and to correlate the SSTR2a positivity and response to SA.
Design: Total 133 cases of GEPNETs(62 pancreas, 12 duodenum, 11 rectum,6 stomach, 17 others and 25 liver metastasis) were subjected to IHC. In brief, formalin-fixed paraffin embedded(FFPE) sections were reacted with anti-SSTR2a(1:1000, Gramsch Laboratories Germany). The staining was graded 0, 1+,2+ and 3+ according to Volante et al.(Modern Pathol 2007). Clinical follow-up was obtained in total 25 cases of SSTR2a 2+ and 3+ cases who were treated with SA, alone or in combination with chemotherapy. The response of the SA therapy was classified into (1)tumor shrinkage,(2)suppression of hormone level,(3)stable disease(SD),(4) increase in tumor size,(5) unknown.
Results: The results of IHC is as follows. Negative-30 cases(22.5%) ,1+ 30 cases(22.5%), 2+ 13 cases(9.8%) and 3+ 60 cases(45.2%.). The overall positive rate(1+2+ 3+), (2+ 3+) was 73.8% or 55% Response to SA in 25 cases was as follows: (1)tumor shrinkage 9 cases:35%,(2) respectively decreased hormone level 2cases:8%,(3)SD 8 cases:32%, (4)increased tumor size 4 cases(16%),(5)unknown 2 cases(8%). 75% of SSTR2a 2+ and 3+ immunoreactivity responded to SA therapy. The increase in size after SA was noted in pancreatic neuroendocrine carcinoma: NEC(1 case),rectal NEC(2 cases) and gastric NEC(1 case).
Conclusions: High proportion of GEPNETs was positive for SSTR2a. 75% of SSTR2a 2+ and 3+ tumors responded to SA therapy. The small proportion of resistant tumors may require other type of targeted therapy such as mTOR inhibitor. This report verifies the SSTR2a immunostaining for the therapeutic benefits of GEPNETs.
Category: Endocrine

Tuesday, March 1, 2011 1:00 PM

Poster Session IV # 51, Tuesday Afternoon


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