(A) Refinement in diagnosis. Among cases of MLBL, the histologic distinction between PMBL, DLBCL and HL may be difficult. (B) Refinement in therapy may include the incorporation of novel biologic targeting agents, involved field radiation, and improved methods of measurement of early response to therapy. MLBL indicates mediastinal large B-cell lymphoma; PMBL, primary mediastinal large B-cell lymphoma; HL, Hodgkin lymphoma; DLBCL, diffuse large B-cell lymphoma; IFRT, involved field radiation therapy; MDD, minimal disseminated disease; and MRD, minimal residual disease.