Heterogeneity of c-myc expression in histologically similar infiltrating ductal carcinomas of the breast.

Anti-c-myc monoclonal antibody was used to evaluate the distribution of the c-myc protein in normal and tumor cells of infiltrating ductal carcinoma. A semi-quantitative method for reporting immunohistochemical assay results (c-myc score) that enables correlations on a more quantitative basis was used in this study. HL-60 cells demonstrated the strongest nuclear staining when fixed in cold acetone (4 degrees C) for 10 min. All 24 specimens of infiltrating ductal carcinomas of the breast and 7 of 11 samples of normal breast tissues studied revealed the presence of c-myc protein. The level of expression in normal breast tissue was much lower than that in breast cancer. Heterogeneity in expression was found within individual tumors and there were substantial differences in the level of expression among different tumors. The subcellular site of staining was predominantly nuclear, occasionally nuclear and cytoplasmic in the same cell, and rarely only cytoplasmic. All four patients with tumor cells located in close proximity to the ductal basement membrane and over-expressing c-myc protein had positive lymph nodes, suggesting that these tumors are more likely to metastasize.