Spectrum of mediastinal B-cell lymphomas. (A) Both PMBL and Hodgkin lymphoma (HL) are putatively derived from a thymic B cell. The events that transform a thymic B cell into PMBL or HL are poorly understood, but there appears to be plasticity in these events, as HL can recur as PMBL and vice versa. (B) Although NSHL is CD15- and CD30-positive and PMBL is CD20-positive, there are mediastinal lymphomas between these 2 entities with histologic and immunohistochemical features intermediate and transitional between NSHL and PMBL. These diseases are MGZLs.