p185(HER2) overexpression in human breast cancer using molecular and immunohistochemical methods

With the successful clinical trials of the engineered antibody Herceptin(TM ) (in advanced-stage breast cancer) and adriamycin-based chemotherapy regim ens (in the adjuvant setting), the need to detect p185(HER2) overexpression or associated amplification of the coding gene HER2 in breast cancer patie nts is escalating. Twenty to 30% of breast carcinomas has overexpression of p185(HER2). This condition correlates with poor patient prognosis and pred icts response to chemotherapy in lymph node-positive patients. In this stud y we compare quantitation of p185(HER2) in breast cancer at the gene and pr otein levels using differential polymerase chain reaction (PCR) and immunoh istochemistry, respectively. To assign HER2 gene copy numbers, a calibratio n curve was constructed using normal breast epithelia and breast carcinoma cell lines having known dosages and amplified HER2. We found corresponding molecular and immunohistochemical results in 85% of the 13 paraffin-embedde d breast carcinoma cases examined. Two cases were found to have minimum gen e amplification but marked p185(HER2) overexpression, suggesting an alterna tive mechanism to overexpression such as transcriptional activation. Althou gh the differential PCR assay exhibits saturation approaching 20 HER2 gene copies, this may not be clinically significant because the immunohistochemi cal assay also appears to saturate in this gene copy number range.