Analysis of c-erbB-2 protein expression in conjunction with DNA content using multiparameter flow cytometry

The relationship between flow-cytometric and immunohistochemically detected c-erbB-2 expression, grade and DNA ploidy in breast cancer

Quantification of c-erbB-2 and its relationship with other prognostic markers using flow cytometry has been examined. In this study a level for c-erbB-2 expression above which tumours are classified as positive by flow cytometry has been determined by employment of positive cut-off threshold levels. c-erbB-2 expression by both flow cytometry and immunohistochemistry was studied using the monoclonal antibody NCL-CBII. The relationship of c-erbB-2 quantification by flow cytometry was then compared with ploidy, axillary node status, tumour size and grade. Increased c-erbB-2 expression was seen using flow cytometry. Correlation between immunohistochemistry and flow-cytometry methods just failed to reach significance (P = 0.06). Immunohistochemistry revealed a significant relationship between c-erbB-2 expression and aneuploidy (P = 0.04). Cytokeratin-positive cells from 110 samples obtained from patients with breast cancer were assayed for DNA content and c-erbB-2 expression by flow cytometry. No correlation was seen between these parameters upon application of Mann Whitney analysis. However, examination of fluorescence thresholds showed a positive correlation between grade and c-erbB-2 expression at a level of more than 3200 molecules (P < or = 0.03). At the level of 3600 molecules significance was increased (P = 0.004). These levels equated with between 15% and 19% of the samples being classified as c-erbB-2-positive. Application of these cut-off points showed no correlation between c-erbB-2 expression and ploidy, tumour size or axillary node status. Comparison of ploidy and grade showed a significant association (P = 0.0015), increased grade correlating with aneuploidy.

Simultaneous analysis of c-erbB-2 expression and DNA content in breast cancer using flow cytometry

The c-erbB-2 oncogene is frequently amplified and overexpressed in human breast cancer. We have studied the c-erbB-2 protein in conjunction with DNA content in frozen samples from breast cancers using flow cytometry. The cell suspensions were obtained by mechanical disaggregation followed by a short fixation in 1% paraformaldehyde. The level of c-erbB-2 expression was calculated as a fluorescence index, taking into account the relative amount of total cellular fluorescence compared to nonspecific fluorescence. The flow cytometric value correlated with immunohistochemical results obtained with the same monoclonal antibody (c-neu, clone 9G6). Overexpression of c-erbB-2 was significantly more frequent in DNA aneuploid tumors than in DNA diploid ones and correlated with increasing S-phase fraction and estrogen receptor negativity. In 10 DNA multiploid tumors, the different aneuploid stemlines uniformly expressed c-erbB-2, supporting the hypothesis that overexpression is an early event in breast cancer. Of the 172 tumors, the 37 (22%) judged as positive with immunohistochemistry showed a somewhat higher rate of distant recurrence than others (P = 0.14). The fluorescence index was significantly associated with prognosis (P = 0.0012), as it was also among the immunohistochemically positive cases. If the degree of overexpression is important, then flow cytometry could be a feasible technique for classification.

Detection of HER-2/neu oncogene amplification in flow cytometry-sorted breast ductal cells by competitive polymerase chain reaction

BACKGROUND

The amplification and/or overexpression of the HER-2/neu oncogene has been proposed as an important prognostic marker in breast cancer. However, contradictory results from various groups regarding whether there is statistical significance in HER-2 amplification or overexpression in predicting overall and disease free survival in node positive versus node negative patients exist in the literature. Current assays on quantifying the HER-2 oncogene rely on DNA extracted from homogenized breast tissue. Not only is a large amount of tissue required, but also, the DNA extract is contaminated with DNA from stromal cells and leukocytes, leading to decreased specificity and sensitivity of the HER-2 assay. Improving the specificity (DNA from breast ductal cells) and the sensitivity (competitive polymerase chain reaction [PCR]) of the HER-2 amplification detection assay will help resolve some of these controversies.

METHODS

Using multiparameter flow cytometry (FCM), ductal cells from breast biopsies and fine needle aspirations (FNAs) are identified and selectively sorted using anti-cytokeratin, anti-HER-2 antibody labeling and DNA staining. HER-2 amplification in these sorted cells is then quantified by competitive DNA PCR using a competitive reference standard mutant template that is susceptible to the restriction enzyme Sma-1.

RESULTS

Applying this strategy, SK-BR-3, an HER-2 amplified breast cancer cell line, was found to have approximately 9x baseline HER-2 oncogene copies. In addition, MCF-7, a known HER-2 nonamplified breast cancer cell line, was found to have baseline HER-2 oncogene copies. In the 10 clinical breast samples tested, 4 of the 10 breast cancers were HER-2 amplified using as few as 1000 cells. The cytokeratin positive cells of these cancers, in contrast to the cytokeratin negative cells, have detectably higher HER-2 amplification (7.2 +/- 2.8x versus 3.2 +/- 1.1x, respectively). Hence, HER-2 gene amplification would have been underestimated if unsorted cells were used because of stromal dilution. In the cytokeratin positive cells that were HER-2 oncogene amplified, corresponding HER-2 oncoprotein overexpression was detected by FCM.

CONCLUSIONS

Using FCM, the ductal cell subpopulation of a breast specimen can be successfully sorted from breast biopsy and FNA specimens. Moreover, by applying the technique of competitive PCR, improved specificity and sensitivity in HER-2 oncogene amplification detection is achieved. The entire procedure can be accomplished in 1 day, allowing for a cost-effective assay and rapid turnaround time.

Sequential paraformaldehyde and methanol fixation for simultaneous flow cytometric analysis of DNA, cell surface proteins, and intracellular proteins

A cell fixation and permeabilization procedure consisting of sequential paraformaldehyde and methanol was evaluated and found suitable for concomitant flow cytometric quantification of total cellular DNA, immunofluorescence measurements of cell surface proteins, and immunofluorescence measurements of intracellular proteins. Paraformaldehyde/methanol-fixed cells exhibited significantly greater intracellular antitubulin immunofluorescence than cells fixed with paraformaldehyde or methanol alone (p less than 0.002) and significantly greater intracellular antitubulin immunofluorescence than cells fixed with methanol followed by paraformaldehyde (p less than 0.006). With paraformaldehyde/methanol fixation, cell morphology was well preserved and forward and right angle light scatter properties were sufficiently well maintained to permit gating on these parameters. Cell surface marker staining with fluorescent anti-leukocyte antibodies was unaffected by fixation with paraformaldehyde/methanol. Paraformaldehyde effects on the intensity of DNA staining with propidium iodide were dependent on paraformaldehyde concentration and fixation temperature; these effects were least pronounced at low paraformaldehyde concentrations (0.25% or less), and at temperatures lower than 37 degrees C. Paraformaldehyde fixation may result in differences in propidium iodide staining of DNA in some diploid cells, which may produce small spurious aneuploid peaks in normal peripheral blood leukocytes. Paraformaldehyde fixation also produces an apparent increase in the DNA index of aneuploid cell populations in comparison with methanol fixation, particularly when the DNA index exceeds 1.5. Occasionally, this paraformaldehyde fixation-induced effect is useful in identifying biologically distinct near-diploid subpopulations in tumors.

Multiparameter flow-cytometric quantitation of epidermal growth factor receptor and c-erbB-2 oncoprotein in normal and neoplastic tissues of the female genital tract

A novel multiparameter flow-cytometric method was used to quantify the expression of epidermal growth factor receptor (EGFR) and c-erbB-2 oncoprotein on 85 cryopreserved normal tissues (30 ovary, 29 endometrium, 16 cervix) and 67 carcinomas (31 ovarian, 18 cervical, 15 endometrial, 3 vulvar). Overexpression of the EGFR and c-erbB-2 oncoproteins was found in respectively 3/31 (9%) and 10/31 (32%) ovarian carcinomas, 13/18 (72%) and 7/18 (38%) cervical carcinomas, and 2/15 (13%) and 2/15 (13%) endometrial carcinomas. Oncoprotein expression was significantly higher in the malignant tumors (for all tumor sites) than in the corresponding normal tissues (P less than 0.034 for all combinations). Aneuploid tumors expressed levels of EGFR and c-erbB-2 oncoprotein significantly higher than those of DNA diploid tumors (P = 0.042 and P = 0.048, respectively). Oncoprotein could be detected in nearly all normal tissues: expression was higher in premenopausal than in postmenopausal patients (EGFR, P = 0.07; c-erbB-2, P less than 0.001). The present study supports the idea that EGFR and c-erbB-2 may play an important role in the autocrine, paracrine, and/or endocrine growth control and differentiation of normal tissues. Alteration in the expression of these oncoproteins is probably involved in malignant transformation and tumorigenesis.