Neratinib metabolites M3, M6, M7, and M11 were studied in binding, enzyme, and uptake, and cellular and nuclear receptor functional assay screens to identify any potential off-target activity. The metabolites inhibited similar targets as neratinib with no apparent new targets that were only inhibited by the metabolites. With the calculated IC50 values in these assays, inhibition of these targets at clinically relevant concentrations in patients is not expected, given that the IC50 values in vitro were approximately ≥ 8-fold higher than the Cmax in patients receiving the recommended dose of 240 mg/day.