[604] HER2 Testing for Gastric Cancer in Latin America.

Olga L Bohn, Nina P Rios, Carlos Luna, Fernando Mena, Sergio Sanchez-Sosa. MetroHealth Medical Center, Cleveland, OH; Christus Muguerza UPAEP Hospital, Puebla, Mexico; Hospital Dr Max Peralta, Cartago, Costa Rica

Background: Trastuzumab is a monoclonal antibody indicated for HER2 positive gastric cancer patients. Accurate assessment of HER2 is essential to determine Trastuzumab use. HER2 overexpression/amplification has been seen in 15-22% of gastric cancers. Gastric cancer mortality is high in Chile, Costa Rica and Ecuador and low in Mexico, Puerto Rico and Cuba. Little is known about HER2 in gastric cancer in Latin America. We tested HER2 status by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) and determined HER2 concordance.
Design: One hundred cases were reviewed (61 Mexico and 39 Costa Rica). Histologic tumor type included 72 intestinal-type, 24 diffuse-type and 4 mixed-type. Thirty four cases were well differentiated, 45 moderately differentiated and 21 poorly differentiated. Fifty nine cases were resections and 41 were biopsies. All tumor specimens were tested by IHC HercepTestTM (Dako, Carpinteria, CA, USA), using scoring system: 0 negative (no staining is observed or membrane staining is observed in <10% of tumor cells), 1+ negative (a faint/barely perceptible membrane staining is detected in >10% of the tumor cells), 2+ equivocal (a weak to moderate complete membrane staining is observed in >10% of the tumor cells, basolateral or U-shape), 3+ strongly positive (a strong complete membrane staining is observed in >10% of tumor cells, basolateral or U-shape). For FISH, tumors were tested by HER2 FISH pharmdxTM (Dako, Carpinteria, CA, USA); a HER2:CEP17 ratio of >2 was defined as positive for HER2 amplification.
Results: Among 100 tumors, 7(7%) were 3+, 8 (8%) were 2+ and 85(85%) were 0/1+; 90 (90%) were FISH non-amplified and 10 (10%) amplified as shown in Table 1.

Table 1. HER2 IHC-FISH
0/1+84185 (85%)
2+628 (8%)
3+077 (7%)
Total90 (90%)10 (10%)100 (100%)

8 out of 10 amplified cases were highly amplified (≥5). Concordance between IHC and FISH was 98.8% for 0/1+ cases, 75% for 2+ cases and 100% for 3+cases.
Conclusions: This study demonstrates a high concordance IHC-FISH in 3+ and 0/1+ cases. Discrepancies in HER2 2+ cases are attributed to tumor type, heterogeneity of the tissue and interpretation of basolateral and U-shape staining.
No differences in HER2 expression are seen among countries with high and low incidence of gastric cancer.
Category: Gastrointestinal

Tuesday, March 1, 2011 9:30 AM

Poster Session III # 154, Tuesday Morning


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