Syndax Pharmaceuticals Inc., of Waltham, Mass., said it completed an $80 million series C financing round led by Fidelity Management & Research Co. and Delos Capital Fund LP with participation from EcoR1 Capital, Orbimed, Jennison Associates (on behalf of certain clients), Tavistock Life Sciences, Arrowpoint Partners, Cormorant Asset Management, Biomed Ventures and undisclosed top-tier mutual funds, as well as existing investors Domain Associates, MPM Capital, RusnanoMedInvest and Forward Ventures.