**6. Monomorphic PTLD vs. polymorphic PTLD**

The term PTLD represents a spectrum of B-cell hyperproliferative states that can be classified as nondestructive PTLD, polymorphic PTLD, monomorphic PTLD, and classical Hodgkin lymphoma, all of which may be associated with Epstein–Barr virus (EBV).

Nondestructive lesions are classified as reactive plasmacytic hyperplasia, florid follicular hyperplasia, and infectious mononucleosis-like PTLD. These lesions are frequently associated with an acute illness similar to mononucleosis, with polyclonal B-cell proliferation, but without evidence of malignant transformation by definition, the lymphoid architecture is preserved.

Polymorphic PTLDs are polyclonal or monoclonal lymphoid infiltrates with evidence of destructive growth patterns including necrosis, destruction of underlying lymphoid architecture, and nuclear atypia. However, polymorphic PTLD does not otherwise meet all criteria for B-cell or T-/NK-cell lymphomas as characterized in immunocompetent patients [1].

Monomorphic PTLDs are monoclonal lymphoid proliferations. Monomorphic PTLD most commonly resembles aggressive B-cell lymphomas such as Burkitt lymphoma/high-grade B-cell lymphoma or diffuse large B-cell lymphoma (DLBCL), as seen in immunocompetent patients. Likewise, classical Hodgkin-like lymphoma variably resembles those observed in immunocompetent patients. Small B-cell lymphomas such as follicular lymphoma, small lymphocytic lymphoma, and EBV-negative marginal zone lymphomas that occur in the posttransplant setting are not characterized as PTLD. A small group of EBV+ MALT lymphoma is now recognized as *bona fide* PTLD [30].
