Quantification of HER2 oncoprotein in fine-needle aspirates of the breast.

Measurements of either HER2 gene overexpression or its gene-coded protein (p185) are clinically useful for predicting prognosis in breast cancer. The measurements are also useful for identifying metastatic breast cancer patients who may benefit from Herceptin treatment. Since fine needle aspiration (FNA) of the breast has become an increasingly popular technique for obtaining tissue specimens, we have developed a sensitive method to quantify p185 in the aspirate. For this procedure, p185 from the cell pellet of FNA is extracted with a buffer containing Triton X-100, and the p185 is measured with an enzyme immunoassay. Most of the malignant breast tumors (N=7) in this study were associated with elevated p185 concentrations (6/7, 319+/-222 U/mg), compared to the p185 concentrations in normal breast tissue (42.8+/-35 U/mg, N=47) or benign lesions (43.1+/-20.2 U/mg, N=22). Quantification of p185 in FNA may improve the assessment of breast cancer patients, revealing whether they are at high risk and may benefit from Herceptin treatment.