Correlation of c-erbB-2 Gene Expression (Detected by FISH) with Membrane Expression of erbB-2 Protein (Detected by IHC) in Patients with Primary Breast Carcinomas

Summary

Background.
Perspective therapy of women with breast carcinoma using Herceptin, a monoclonal antibody against a membrane protein of the tumor cells, erbB-2 (Her2/neu), requires a precise evaluation of the intensity of erbB-2 protein expression. Overexpression of the erbB-2 protein is associated with an overexpression of the c-erbB-2 gene, most frequently with the gene amplification. This relation is not sufficiently verified to be used in clinically applied diagnostics. Immunohistochemical (IHC) detection of the membrane expression of the erbB-2 protein is not always reliable. The aim of the study was to determine the relation of the protein expression and the c-erbB-2 gene copy number and to ascertain whether in cases with controversial IHC of erbB-2 protein investigation of the gene copy numbers would help to decide if the Herceptin treatment is indicated.Methods and Results. We investigated 34 patients with breast carcinoma in a pilot study. The average age of the patients was 59 years (median 57 years), with the range from 33 years to 88 years. In all cases we investigated the tissue from primary breast carcinomas prior to oncology treatment. The number of c-erbB-2 gene copies was evaluated using fluorescence in situ hybridization (FISH). The membrane expression of the erbB-2 protein was expression of hormonal receptors, and with the findings in the axillary lymph nodes. The carcinomas were divided according to the number of c-erbB-2 gene copies in three groups. The first group (7 patients) was characterized by more than 10 copies of c-erbB-2 gene in the tumor cell nuclei (strong amplification). In the second group (9 patients) there were carcinomas with less than 10 copies of the c-erbB-2 gene. The third group (18 patients) formed carcinomas without c-erbB-2 gene amplification. Best correlation of the c-erbB-2 gene status with the erbB-2 protein expression was found for the group 1 (strong gene amplification, strong protein expression). The morphology was that of invasive duct carcinoma, in 6 of 7 patients grade 3. Estrogen and progesterone receptors were negative in a majority of the patients. In five of the seven patients axillary lymph node metastases were detected. In group 2 and 3 with low c-erbB-2 gene copy numbers the erbB-2 protein expression was moderate, weak or negative. The patients had carcinomas of variable grades (predominantly grade 2) and had a variable expression of the hormonal receptors. No significant association with lymph node metastases was found.Conclusions. Invasive duct carcinoma of the breast with a strong amplification of the c-erbB-2 gene have a strong expression of the membrane protein erbB-2. There is a direct relation between amplification of the c-erbB-2 gene with more than 10 copy numbers and a strong overexpression of the erbB-2 protein. Our results show that breast carcinomas with a strong c-erbB-2 gene amplification have more aggressive features than carcinomas with a lower number of c-erbB-2 gene copies or carcinomas with two signals of c-erbB-2 gene. Expression of the membrane protein erbB-2 in a carcinoma with a low amplification or without the c-erbB-2 gene amplification is weak or negative. However, a weak positivity or negative IHC result may be caused by technical problems (e.g. fixation of the tissue). Therefore, the assessment of the copy numbers of the c-erbB-2 gene is a matter of choice in cases of weak and difficult to interpret results of erbB-2 protein detection.

Key words:
breast carcinoma, c-erbB-2 gene amplification, erbB-2 protein overexpression, grade, metastases, hormonal receptors