Syndax Pharmaceuticals announced positive results from its Phase 2 study of exemestane with and without entinostat for the treatment of advanced breast cancer. ENCORE 301, a multicenter, randomized, double-blind, placebo-controlled study hit its primary endpoint of an improvement in progression-free survival (PFS). In the intent-to-treat (ITT) population, PFS was significantly longer (defined prospectively as one-sided P<0.10) with exemestane + entinostat than with exemestane + placebo (4.28 vs 2.27 months, respectively; HR=0.73; P=0.06). The ITT population, with a median follow-up of 18 months, had significantly longer overall survival with exemestane + entinostat than with exemestane + placebo (26.94 vs 20.33 months, respectively; HR=0.56; P=0.027). In the subset of entinostat patients with protein acetylation data (n=27), median PFS increased to over six months in the patients exhibiting protein lysine hyperacetylation. Entinostat combined with exemestane was well tolerated with the most frequent adverse events consisting of fatigue, gastrointestinal disturbances and hematologic abnormalities.

Entinostat is a novel, oral small molecule inhibitor of class I histone deacetylases, key enzymes that alter the structure of chromatin to control gene expression. 

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