Berkeley, CA, December 12, 2011 -- Plexxikon Inc., a member of Daiichi Sankyo Group, today announced scientific findings from preclinical studies showing that treatment with a novel oral agent, PLX3397, selectively inhibited key cancer-driving Flt3 mutations that occur in 20-30 percent of acute myeloid leukemia (AML) patients. In a preclinical model of AML, PLX3397 showed significant tumor regression. This preclinical work also showed that PLX3397 retained activity against certain drug-resistant forms of mutated Flt3 that can occur with other treatments. These scientific findings were presented during the American Society of Hematology (ASH) Conference, taking place December 10-13, 2011 in San Diego (Abstracts #764 and #3632). Plexxikon recently initiated a Phase 1/2 study in AML patients, further described at www.clinicaltrials.gov.