Morphological characteristics of PTFL, PNMZL and cases with overlapping features. (A-B) Two examples of typical PTFL with expanded, serpiginous germinal centers with a starry-sky pattern and attenuated mantle zones. Note in panel A, a rim of normal lymph node at the upper edge of the biopsy specimen. (C) IgD stain highlights the attenuated mantle zone. (D) PNMZL with overlapping features with PTFL, Case 28. The lymph node shows large, irregular germinal centers with attenuated marginal zones together with expanded interfollicular areas. (E) Case 19. The lymph node reveals an infiltrate with nodular pattern with recognizable hyperplastic germinal centers and expanded mantle zones with marginal differentiation. (F) IgD stain shows the extension of the mantle zone B cells into the germinal centers, which display fragmentation, resembling progressively transformed germinal centers (PTGC). (G-L) PNMZL with PTGC-like features.Case 40. (G) Lymph node with residual reactive follicles but the interfollicular region is markedly expanded. (H) The cellular infiltrate is polymorphous with occasional plasma cells and immunoblasts. (I) A stain for CD20 shows a predominance of B cells surrounding a residual follicle. (J) IgD stain shows the intact mantle cuff. The germinal center exhibits some fragmentation reminiscent of PTGC. (K) The residual germinal centers are positive for CD10 and negative in the atypical cells. (L) BCL2 is negative in germinal centers but positive in interfollicular cells.