Figure 1.

Activation of the PI3K pathway was more significantly associated with trastuzumab resistance than PTEN status alone. A: Heterogeneous expression of the PTEN protein in invasive ductal carcinoma lesions examined by IHC in HER2-positive MBC tumors. B: Representative PTEN IHC staining (IRS = 0, 3, 12). Arrows point to fibroblasts and endothelial cells that showed high expression of PTEN, which served as an internal positive control. C: Poor response (P = 0.081) and significantly shorter OS (P = 0.023) after trastuzumab-based therapy in patients with PTEN loss alone (PTEN loss defined as IRS ≤3). D: Significantly poorer response (P = 0.047) and shorter OS (P = 0.015) after trastuzumab-based therapy in patients with PI3K pathway activation (defined as PTEN loss and/or PIK3CA mutation). Scale bar = 50 μm.