In particular, an innovative and rapid development of a targeted mass spectrometric-based assay to assess a response prediction signature was highly warranted as neither baseline HER2 or HER3 protein expression (as measured by IHC) nor Heregulin mRNA expression (as measured by PCR) were associated with clinical response to lumretuzumab in Breast Cancer [16]. Here, NRG1 is linked to breast carcinoma.