[595] HER2 Assessment in Gastric Cancer Surgical Specimens: Proposal of a Work-Flow for Practical Routine Use.

Sofia Asioli, Francesca Maletta, Ludovica Verdun di Cantogno, Maria A Satolli, Marina Schena, Carla Pecchioni, Cristina Botta, Giulia D'Angelo, Daniele Recupero, Giuseppe Ingravallo, Eugenio Maiorano, Anna Sapino. University of Turin, Italy; University of Bari, Italy

Background: In gastric cancer (GC) the expression of HER2 is known as a marker of prognosis and recently it has been confirmed as a predictive marker of response to Trastuzumab.
Design: GC specimens of 100 patients were collected. Representative samples from both primary tumors (100 samples) and lymph node metastases (24 samples), were selected. In each case, 4B5 (Ventana), CB11 (kit Oracle Menarini), HercepTest (Dako) antibodies were tested in immunohistochemistry (IHC) and scored as proposed. HER2 gene status was studied by double probe fluorescence in situ hybridization (FISH) in all cases. Concordance among IHC scoring results of the 3 antibodies and between FISH results and IHC (0/1+ and 2+/3+), independently from the percentage of positive cells, were evaluated using the Cohen-Fleiss' kappa statistic (K). The number of specimens needed to be tested in cases with <10% of HER2 overexpression was assessed. Finally, influence of gain of CEP17 (copies number >3) on the results of FISH ratio was considered.
Results: The 3 antibodies showed a K of 84% (p<0,05). The overall concordance of FISH/IHC was >80% (p<0,05) in the primary tumor and was >85% (p<0,05) when correlated with lymph node metastases for the 3 antibodies. Nine cases showed 2+/3+ in <10% of cells which corresponded to a IHC score value of 0. In 8 of these cases the percentage increased to >10% adding 2 more sections from different tissue blocks of the primary tumor. In our case series, the gain of CEP17 did not influence the final score ratio of FISH analysis.
Conclusions: The HER2 analysis of surgical specimens of GC has to consider the tumor heterogeneity. When the IHC score is 0/1+ on 1 tissue block, we recommend to test 2 more tissue blocks, particularly in the cases were the negative score is related to the low percentage of positive cells (<10%). Our work flow protocol avoids working over-load and solves equivocal cases.
Category: Gastrointestinal

Tuesday, March 1, 2011 11:15 AM

Platform Session: Section E, Tuesday Morning


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