Additional Study Information: We are testing new experimental drugs such as selinexor in the hopes of finding a treatment that may be effective against tumors that have come back or that have not responded to standard therapy. The goals of this study are: To find the highest safe dose of selinexor that can be given without causing severe side effects; To learn what kind of side effects selinexor can cause; To learn more about the pharmacology (how your body handles the drug) of selinexor; To learn more about the biology of selinexor in blood and tumor tissue; To determine whether selinexor is a beneficial treatment for your tumor.