PTLD Classification of 1981 (Frizzera et al.)
Category	Follicular Center Cells	Plasmacytic Cells	Large Lymphoid Cells	Atypical Immunoblasts	Invasion	Necrosis
Nonspecific Reactive hyperplasia	++ (Germinal Centers)	++	+/++	No	No	No
Polymorphic Diffuse B Cell Hyperplasia	++ (Diffuse)	++	++/+++	No	+	No
Polymorphic Diffuse B Cell Lymphoma	++ (Diffuse)	+	++/+++	+/+++	+	+++
Immunoblastic Sarcoma of B Cells	No	+	+++	+/+++	+	+

Reference Frizzera G, Hanto DW, Gajl-Peczalska KJ, Rosai J, McKenna RW, Sibley RK, Holahan KP, Lindquist LL: Polymorphic Diffuse B-Cell Hyperplasias and Lymphomas in Renal Transplant Recipients. Cancer Res 41:4262-4279, 1981.

University of Pittsburgh.