Determination of HER2 by fluorescence in situ hybridization (FISH) in breast cancer. Experience of the Reference Laboratory of Lisbon.

Abstract

The knowledgement of HER2/c-erbB-2 status in breast cancer is essential for the eligibility of the patients for therapy with monoclonal antibody anti-HER-2/trastuzumab. From the various existent techniques for the determination of HER-2, the most widely used are: immunohistochemistry (IHC), that estimates the protein expression, and in situ hybridization (FISH), that evaluates its amplification. FISH is essential as complementary of IHQ in tumors with equivocal or non interpreted staining, and also in those with complete weak to moderate membrane staining in >10 % of neoplastic cells (score 2+) because, of these, only cases with gene amplification (FISH positive) respond to therapy. Recent studies also support that FISH should be performed in cases with score 3+, because 10-12% of them don't have amplification. The expensive equipment and reagents for standard FISH method and the need of extensive training and expertise for both the technique and the evaluation, justify a centralized testing in Reference Laboratories. Our aim was to describe the work of the Department of Pathology of the Portuguese Institute of Oncology of Lisbon as a Reference Laboratory in the execution of FISH technique and to present the results obtained from May 2001 to August 2004. FISH was performed with Kit INFORM HER2/neu Gene Detection System, using the BenckMark system of Ventana. We evaluated a series of 4499 invasive carcinoma primary of the breast, that included 587 cases of the Portuguese Institute of Oncology of Lisboa and 3912 cases from different Hospitals of Lisboa, Cascais, Almada, Barreiro, Santarém, Evora, Faro, Portimão, Guimarães, Funchal and Angra do Heroísmo. We verified that 591 cases (13.5%) had HER2 gene amplification, being those patients eligible for therapy with trastuzumab.