Locally advanced rectal cancer (T3, T4 or lymph node positive tumors) are conventionally treated with 5FU / capecitabine based chemoradiation prior to surgical resection. This treatment is associated with only a 15-20% pathological complete response. Selinexor (KPT-330) is a Selective Inhibitor of Nuclear Export (SINE) XPO1 antagonist that has demonstrated radiosensitization with in vivo models and has suggested single agent activity against colorectal cancers in a Phase I trial. Here we perform a Phase I/Ib trial of standard chemoradiation combined with Selinexor.