This is an open label, multicenter, dose escalation, phase Ib study to determine the recommended phase II dose (RP2D), by assessing the maximum tolerated dose (MTD), safety and preliminary efficacy of selinexor in adult patients with relapsed/refractory B-cell malignancies receiving either R-DHAOx (Group A) or R-GDP (Group B). This dose escalation phase will be followed by an exploratory expansion phase in the same population with 12 patients enrolled in each group, who will receive selinexor at the RP2D.