It is hypothesized that lapatinib-induced liver injury is caused by HLA-mediated antigen presentation to CD4 positive T cells. However, analysis of PBMC and cloned T-cells from patients with HLA-DRB1*07:01-restricted lapatinib-induced liver injury revealed no evidence for drug-specific activation. T cells were exposed to lapatinib, the M11 aldehyde, and quinone imine [oxidized form of hydroquinone amine M1] metabolites. Reactivity of the quinone imine was confirmed by mass spectrometry.