HER-2/neu in breast cancer: a comparative study between histology, immunohistochemistry, and molecular technique (FISH)

HER-2/neu is a protooncogene frequently overexpressed in breast cancer. Fluorescence in situ hybridization (FISH) is a technique targeting the gene amplification, while immunohisto-chemistry detects the protein expression. Usually both are applied to paraffin-embedded tissue. The authors studied HER-2 by FISH and immunohistochemistry (HercepTest) in 81 breast carcinomas. The results showed an overall concordance (correlation coefficient 0.64). In all cases with HercepTest score 0 and 1+, nonamplification of the gene was observed. Gene amplification was found in 20% of cases with a 2+ score and in 77.78% of cases with a 3+ score. Data described in literature for 3+ carcinomas showed a 3% to 10% discrepancy between protein expression and gene amplification, while in this study this difference was up to 22.22%. As a consequence, even if it is usually considered important to analyze only 2+ cases by FISH, 3+ scores nonamplified for HER-2/neu may be a new, interesting subset. Furthermore, the authors investigated the two-variables correlation between chromosome 17 copy number, protein over-expression, gene amplification, and presence of metastatic lymph nodes. Interesting results came from the correlation between the HercepTest score and the HER-2/neu gene amplification evaluation, HercepTest and chromosome 17 aneusomy, and gene amplification and lymph nodes status. In conclusion, the FISH technique can be an important and useful diagnostic tool to integrate the results of the HercepTest and to select patients for immunotherapy.

High-level detection of gene amplification and chromosome aneuploidy in extracted nuclei from paraffin-embedded tissue of human cancer using FISH: a new approach for retrospective studies

A novel application of fluorescence in situ hybridization (FISH) to isolated nuclei is described. The method detects gene amplification and chromosome aneuploidy in extracted nuclei from paraffin-embedded tissue of human cancer with greater sensitivity and specificity than existing FISH methods. In this study, the method is applied to signal detection of the HER-2/neu (c-erbB-2) gene, whose amplification is one of the most common genetic alterations associated with human breast cancer. Nuclei were extracted and isolated from formalin fixed, paraffin embedded tissue of 43 different carcinomas (breast, ovary, endometrium, gastrointestinal stromal tumor and malignant mesothelioma). FISH was performed both on sections and extracted nuclei of each tissue using chromosome enumeration probes (CEP) for the centromeric regions of chromosomes 8 and 17, and a locus specific identifier (LSI) for the HER-2/neu oncogene. Differences between ploidy calculated in sections and extracted nuclei were seen in 3 breast carcinomas and 1 gastrointestinal stromal tumor (GIST). Furthermore, 1 breast cancer, previously considered to be borderline for HER-2/neu gene amplification turned out to be clearly amplified. Nuclei extraction and isolation bypass all the problems related to signal interpretation in tissue sections, and the adoption of this new technique, which improves the signal quality in several neoplastic samples, is suggested.

[DNA flow cytometry. Comparison of the methods for nuclear extraction from frozen and paraffin-embedded sections]

Cellular DNA content of solid tumors can be determined either from fresh, frozen, or formalin fixed, paraffin-embedded tissues. However, discordant results have been obtained using the paraffin-embedded technique, and lack of abnormal DNA stemlines in the paraffin-embedded as compared to either fresh or frozen tissues has been reported. In this study we evaluated the validity of nuclear extraction method from paraffin-embedded tissues, using 75 breast carcinomas whose DNA content was previously analyzed from frozen tissue and resulted either normal (12 cases) or abnormal (63 cases). From representative paraffin blocks, nuclei were extracted following Hedley's technique. The results revealed excellent cell counting and good histogram resolution from all paraffin samples; the loss of G2M abnormal peak in eight histograms with abnormal stemline did not compromise the correct interpretation of DNA content. In addition, the comparison between DNA indices obtained from corresponding paraffin and frozen samples showed a good correlation in 69 cases (r = 94); discordance in six cases was demonstrated to be related to tumor heterogeneity. In conclusion the paraffin extraction method is a sensible, and reliable technique, which can be applied for DNA flow cytometric studies on archival cases, as well as whenever fresh sample from the tumor is not obtainable.

Usefulness of the scraping method for DNA flow cytometry in breast tumors

Flow cytometric DNA analysis is an important prognostic tool in breast cancer. We evaluated the possibility of performing DNA analysis on cell suspensions obtained by scraping the cut surface of breast tumors; 31 breast tumor nodules, including six benign and 25 malignant lesions, were studied. From each case, cell suspensions acquired by mechanical mincing of a fresh frozen tissue fragment and by two different scrapings (central and peripheral) from the cut surface of the tumor were analyzed via flow cytometry. In all cases, comparison of the DNA histograms for three samples showed no significant differences in the appearance of debris or in the value of coefficient of variation of the G0-G1 peak. All benign nodules showed a normal DNA stemline in all specimens. In 23 of 25 cases of breast carcinoma, the ploidy of the three preparations was similar, with a concordance in 12/14 (85, 71%) cases in DNA nondiploid tumors. Linear regression analysis showed a good correlation in DNA index between either scraping sample and the tissue fragment (r = .955 and r = .905). The results indicate that the scraping technique provides excellent cell suspensions and DNA histograms comparable to those obtained from mechanical mincing of tissue fragments. The technique minimizes preparation time and avoids consuming much tissue and, thus, is the method of choice when very small cancers have to be analyzed.