TAS2940 fumarate is a brain-penetrable, orally active, irreversible and selective pan-ERBB inhibitor. TAS2940 fumarateagainst wild-type HER2, HER2 V777L, and A775_G776insYVMA with IC 50 values of 5.6 nM, 2.1 nM, and 1.0 nM, respectively. TAS2940 fumarate can be used for the study of tumors with HER2 and EGFR aberrations.