World Health Organization PTLD Classification of 2001
Category	Examples	Histopathology	Immunophenotype	Clonal Status	Oncogene, Tumor Suppressor Gene Changes	Comments
"Early" lesions	Reactive plasmacytic hyperplasia (PH) infectious mononucleosis-like PTLD	Some architectural preservation; numerous plasma cells and lymphocytes;variable paracortical expansion; many immunoblasts may be present; atypia slight; some cases may have overlapping features of PH and IM-PTLD	Polyclonal B cells, plasma cells and T cells. Immunoblasts often EBV-positive	Polyclonal; EBV present in most case of PH- IM cases typically EBV positive, may have minor monoclonal or oligoclonal bands	(None)	Often regress with reduced immunosuppression, severe cases may be fatal Examples of posttransplant plasmacytic hyperplasia without EBV should not be considered as PTLD.
Polymorphic PTLD	Polymorphic B cell hyperplasia, Polymorphic B cell lymphoma	Destruction of underlying architecture, full range of B-cell maturation seen, may have necrosis, scattered large bizarre cells (atypical immunoblasts), frequent mitoses, may have monomorphic areas	Mixture of B and T lymphocytes, surface and cytoplasmic Ig polytypic or monotypic; most cases EBV positive	Monoclonal; Rare cases may be polyclonal	None	Overall impression of mixed small and large cell lymphoma or polymorphous immunocytoma; may be multiple; Some cases regress with reduced immunosuppression, others may progress
Monomorphic PTLD	B-cell neoplasms: Diffuse large B-cell lymphoma, Burkitt's or Burkitt-like lymphoma, plasma cell myeloma, plasmacytoma-like lesions T-cell neoplasms: Peripheral T-cell lymphoma, not otherwise specified; other types	Morphological lymphomas; classify according to current lymphoma categorization; most to all cells transformed, blastic (plasma cell leisons excepted); most look like diffuse large B-cell lymphoma, other types less common; Monomorphic T-cell PTLD probably inlcudes most or all types of T-cell neoplasms	B cell PTLD show CD19, 20, 79a; monotypic Ig expressoin in 50%; Many express CD43, CD45RO (due to upregulation of these T cell markers in B cells harboring EBV); CD30 often postive; most EBV pos. T cell PTLD may express CD4 or 8, CD56, CD30, and alpha-beta or gamma-delta T-cell receptors	Monoclonal Ig genes in B cell PTLD; EBV pos. cases also have clonal EBV; T cell PTLD usu. have clonal T cell receptor; 25% with clonal EBV	Present in some cases	Recommended that these be classified according to standard lymphoma classification, with term " PTLD" added; Monomorphism means that most cells are transformed- cellular monotony may be present but is not required; Regression possible but uncommon compared to early lesions and polymorphic PTLD. Overall mortality 60% solid organ, 80% marrow recipients.
Hodgkin lymphoma and Hodgkin lymphoma-like PTLD	Classic HL; Hodgkin-like PTLD	Reed Sternberg cells in appropriate backgound (see comments)	Classic HD CD15, CD30 pos; HD-like PTLD more atypical phenotype, usu B cell antigens expressed; all or almost all cases EBV pos (HD and HD-like)	--	--	Since Reed-Sternberg-like cells can be seen in polymorphic PTLD, diagnosis requires appropriate morphologic and immunophenotypic features

Reference Harris NL, Swerdlow SH, Frizzera G, Knowles DM: Post-transplant lymphoproliferative disorders. in: Jaffe ES, Harris NL, Stein H, Vardiman JW (eds): World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissues. IARC Press: Lyon, pp. 264-269, 2001

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