Formalin-fixed paraffin-embedded tumour specimens from 118 HER2-overexpressing breast cancer patients treated with radical local therapy and trastuzumab in adjuvant setting were used for the assessment of: (1) PIK3CA gene mutations (p.H1047R and p.E545K) by qPCR, and (2) expression of Ki-67, EGFR, MUC4, HER3 and PTEN by immunohistochemistry.
We further validated the approach in breast cancer cells with mutational activation of PIK3CA, where tandem mass spectrometry detected and quantitatively measured the abundance of a helical domain mutant (E545K) of PIK3CA connected to PI3K activation.