Protocol for PTEN expression by immunohistochemistry in formalin-fixed paraffin-embedded human breast carcinoma

The PI3K/PTEN pathway plays a major role in carcinogenesis. Dysregulation of this pathway occurs frequently in breast cancer, and loss of PTEN expression is emerging as a potentially important mechanism of resistance to the widely used anti-HER2 therapy, trastuzumab. However, assays for loss of PTEN expression have suffered from lack of consistency. Here, we describe an automated and reliable protocol for PTEN protein expression by immunohistochemistry in formalin-fixed paraffin-embedded tissue that can be easily incorporated into clinical trials.