OBJECTIVETo deduce the protocol, scoring criteria and interpretive guidelines for assessment of HER2 gene expression status by fluorescence in-situ hybridization (FISH) and to compare the results with those obtained by immunohistochemistry.

METHODSThe HercepTest kit from Dako Cytomation was employed for immunohistochemistry. FISH for HER2 gene expression status was performed using PathVysion DNA probe kit on the archival paraffin-embedded sections of breast cancer tissues from 28 Chinese female patients with immunohistochemical staining scores of (3 +), (2 +), (1 +) and 0.

RESULTSTen of the 12 patients with score (3 +) by immunohistochemistry were positive for HER2 by FISH, with 2 cases being polysomy. Two other cases with FISH-negative were also shown to be polysomy. Seven of the 10 patients with score (2 +) by immunohistochemistry showed HER2 gene amplification, with 1 case being polysomy. Two of the remaining 3 cases, which were FISH-negative, were shown to be polysomy. All the patients with scores (1 +, number = 3 ) or 0 ( number = 3) by immunohistochemistry failed to show amplification. One case of polysomy was noted in either group.

CONCLUSIONSImmunohistochemistry is useful as an initial screening tool for HER2 expression status. Because of the obvious discrepancies between protein expression and gene amplification, patients with score (2 +) by immunohistochemistry should undergo FISH testing as well. FISH is also required in selected examples with score (3 +) immunohistochemical results, especially in those with false-positive immunohistochemistry due to chromosome 17 aneuploidy.