An orally active, selective MEK inhibitor with potential antineoplastic activity. MEK inhibitor AZD8330 specifically inhibits mitogen-activated protein kinase kinase 1 (MEK or MAP/ERK kinase1), resulting in inhibition of growth factor-mediated cell signaling and tumor cell proliferation. MEK 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.