[Evaluation of HER2 gene expression status in breast cancer by fluorescence in-situ hybridization].

Objective: To 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.

Methods: The 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.

Results: Ten 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.

Conclusions: Immunohistochemistry 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.