Morphologic spectrum of PTLD. (A-C) PTLD, early lesion, plasmacytic hyperplasia. (A) In a preserved underlying architecture, there is a proliferation of small reactive plasma cells (inset). Immunohistochemical staining against κ (B) and λ (C) light chains shows the polytypic character of the plasma cells. (D-F) PTLD, polymorphic. (D) Lymph node architecture is effaced by a polymorphic proliferation of B cells of variable size, shape, and degree of transformation (HRS-like cell shown in inset), which are admixed with numerous small lymphocytes, plasma cells, eosinophils, and histiocytes. (E) Immunohistochemical staining against CD20 shows membranous and often Golgi-type expression in the B blasts. (F) Epstein-Barr virus–encoded RNA in situ hybridization shows nuclear positivity not only in the HRS-like cells but also in a variety of B cells. (G-I) PTLD, monomorphic, EBV⁺ DLBCL. (G) Monotonous proliferation of large transformed B cells (inset) with an infiltrative growth pattern and mitotic activity. (H) Diffuse CD20 expression of the infiltrate corresponding to the B-cell phenotype. (I) Most cells are EBV⁺, as seen in this Epstein-Barr virus–encoded RNA in situ hybridization. Images were taken with a Leica DFC290. Bars represent 50 µm. Original magnification 630×. Hematoxylin and eosin stain. HRS, Hodgkin/Reed-Sternberg.