HER-2 status determination in breast carcinomas. A practical approach

Accurate evaluation of HER-2 status is crucial in the selection of breast carcinoma patients for trastuzumab (Herceptin) treatment. Various laboratory methods have been used for this purpose. The aim of the present work was to analyse the results obtained in the routine practice by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) in determination of HER-2 status. Five hundred and three cases of breast invasive ductal carcinoma were selected to analyse the HER-2 overexpression by immunohistochemistry (HercepTest, Dako). HercepTest 2+ equivocal cases (60) were studied by FISH (PathVysion, Vysis) to determine HER-2 gene amplification. HER-2 overexpression determined by Herceptest was shown in 97/503 cases (19%). FISH performed on equivocal cases demonstrated HER-2 amplification in 11/60 tumours (18%). IHC and FISH together showed HER-2 overexpression/gene amplification in 21% of breast invasive carcinomas. Immunohistochemical determination of HER-2 status represents an easy and standardized method that (in contrast to FISH) can be performed in all pathology laboratories without need of any special microscope and enabling to check the morphologic features of the cells analysed. However, in order to assure the reliability of the results, standardization of fixation protocols, automation of the immunohistochemical procedure, and training of pathologists in the interpretation of the results (scoring criteria) should be a priority. Equivocal HercepTest cases must be analysed by FISH preferably in a reference laboratory.