An orally bioavailable selective MEK inhibitor with potential antineoplastic activity. Refametinib specifically inhibits mitogen-activated protein kinase kinase 1 (MAP2K1 or MAPK/ERK kinase 1), resulting in inhibition of growth factor-mediated cell signaling and tumor cell proliferation. MEK, a dual specificity threonine/tyrosine kinase, is a key component of the RAS/RAF/MEK/ERK signaling pathway that regulates cell growth; constitutive activation of this pathway has been implicated in many cancers.