Correlation of Heregulin mRNA and Her-2/neu Protein Expression with Node Metastasis and DNA Ploidy Pattern in Human Invasive Breast Carcinoma

ABSTRACT

The Her-2/neu protooncogene encodes a transmembrane tyrosine kinase that is structurally homologous to the receptor for epidermal growth factor. Its amplification and overexpression are associated with poor prognosis in breast cancer patients. Neu differentiation factor is a ligand for Her-2/neu protooncogene and was detected in ras-transformed rat fibroblasts. Heregulin (human homologue of neu differentiation factor) is a 44-kilodalton glycoprotein that stimulates tyrosine phosphorylation and induces growth arrest or stimulation and differentiation in human breast cancer cell lines. In this study we examined the expression of heregulin mRNA by nested reverse transcription (RT) PCR with fresh tissue, Her-2/neu protein, ICAM-1 and steroid receptors by immunohistochemistry, and DNA ploidy pattern by flow cytometry with paraffin-embedded tissue in invasive breast carcinoma. We compared the data with nodal status, lymphovascular invasion, steroid receptor status and DNA ploidy pattern. For RT-PCR to heregulin mRNA, 38 cases of fresh breast cancer tissue were obtained. Total 68 cases of invasive breast carcinoma tissue were fixed in formalin, which were used for routine histology, immunohistochemistry and flow cytometry. The results are as follows; 1) Heregulin mRNA was expressed in 86.1% of patients with invasive breast carcinoma and 100% of patients with benign breast lesion using nested RT-PCR analysis. 2) Her-2/neu protein was overexpressed in 50.0% of tumors using immunohistochemistry. The expression of Her-2/neu protein was significantly correlated with high counts of lymph nodes with metastasis (p<0.05), and high nuclear grade (p<0.05). 3) Her-2/neu protein overexpression was significantly correlated with a high DNA index(p<0.05). All of the tumors showing Her-2/neu protein overexpression and no heregulin mRNA expression revealed near tetraploid DNA content. However, both Her-2/neu overexpression and heregulin mRNA expressing tumors revealed near tetraploidy in 38.9% and diploidy in 50.0%. Based on these results, heregulin mRNA expression rate was 86.1% in human invasive breast carcinoma. Her-2/neu protein overexpression is associated with high positive lymph node number and DNA index. Statistically significant reverse correlation with lymph node metastasis is not present.