Quantum dot-labelled antibody to quantify expression of the EGF family of receptors and ligands in breast cancer specimens

The epidermal growth factor receptors (ErhBl, ErbB2, ErbB3 and ErbB4) have become an attractive target for drug development. In particular ErbB2 is one of the most important biomarkers routinely used to predict breast cancer patients' response to Herceptin, an effective drug for the treatment of breast cancers expressing high levels of ErbB2. The current techniques in clinical use for the assessment of ErbB2 are immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH); however both. IHC and FISH have several limitations which may result in patient misclassification. Using Quantum dots (Qdot) labelled antibodies, laser scanning confocal microscopy and image segmentation techniques, we have developed a new system which provides a more linear and scalable quantification of ErbB2 expression in formalin fixed paraffin embedded breast cancers. We first demonstrated that the Qdot system could reliably detect ErbB2 expression in IHC 3+ and 2+ cases on a tissue microarray containing 60 samples of formalin fixed paraffin embedded breast cancer sections. We then apply the system to quantify ErbB2 expression in 145 primary breast cancers treated with Herceptin, all previously classified as 3+ or 2+ by IHC or FISH positive. A comparison of immunofluorescent staining with conventional immunohistochemistry showed that the Qdot system gives more linear and scalable measurements of receptor levels. In both breast tumour sets the system detected very different levels of ErbB2 expression extending over a sixty fold range. We have evaluated the correlation between ErbB2 receptor levels, measured by Qdots, and patient's response to Herceptin. These preliminary data showed better survival in the high ErbB2 expressing cases which is consistent with the hypothesis that Herceptin has a greater benefit in patients with high ErbB2 levels.