High Incidence of Immunohistochemical SSTR2a Expression in Gastro-Entero-Pancreatic Neuroendocrine Tumors (GEPNETs): Studies on Primary and Metastatic Diseases
H Hirabayashi, C Inomoto, K Hirabayashi, RY Osamura. Tokai University School of Medicine, Isehara, Kanagawa, Japan
Background: It has been widely known that immunohistochemical expression of SSTR2a is directly related to the clinical response of somatostatin analogue(SA) in GEPNETs. This report is aimed at to elucidate the general incidence of SSTR2a positivity and that in the metastatic NEC in the liver. Staining intensity was compared with MIB-1 proliferative indices.
Design: Total 81 tumors were studied. 66 primary GEPNETs (46 pancreas, 10 duodenum, 7 rectum, 3 stomach) and 15 metastatic GEPNECs (11 cases of pancreatic NEC, 2 cases of rectal NEC and 1 case of duodenal NEC) were subjected to immunohistochemical staining for SSTR2a on formalin-fixed paraffin embedded(FFPE) sections. We used anti-SSTR2a antibody (Gramsch Co) and polimer method. MIB-1 was stained with antibody (DAKO Co) combined by polymer method.
Results: Immunohistochemical staining for SSTR2a on cell membrane of tumor cells was graded to 0:negative, 1+:weak, 2+:intermediate,3+:intense. In total numbers of cases, 76% of the cases showed 1+ to 3+ positive staining. 45.4% of cases revealed 3+ staining . 15 cases of metastatic GEPNECs in the liver showed the positive rate of SSTR2a 1+-3+ with 80% and 3+ with 67%. In 9 cases of metastases, MIB-1 index was higher than 10%(grade 2 by WHO) in 4 cases. There was no correlation between MIB-1 indices and SSTR2a staining.
Conclusions: In general, 76% of GEPNETs showed positive SSTR2a. Especially, the cases with liver metastases showed higher positive rate and more intense staining for SSTR2a and are expected to respond to SA.
Tuesday, March 23, 2010 1:00 PM
Poster Session IV # 53, Tuesday Afternoon