Figure 1.

Histopathological and immunohistochemical investigations of lymph node (LN) biopsies in case 1. A, A cervical LN showing a florid B‐cell and plasmacytic infiltrate mimicking nodal marginal zone lymphoma (NMZL)/secondary NMZL, obscuring underlying angioimmunoblastic T‐cell lymphoma (AITL). Upper panels: on an haematoxylin and eosin (H&E)‐stained section (left), there is effacement of the nodal architecture by an expanded perifollicular infiltrate (right) composed of small and medium‐sized lymphocytes and mature plasma cells. Middle panels: CD79a staining highlights the B cells and plasma cells (left), whereas CD138 marks the dense clusters of mature plasma cells (right). Lower panels: there is an increase in the number of programmed cell death protein 1 (PD1)‐positive T cells within the germinal centres (strong staining) and also in the perifollicular areas (left), but CD21 staining does not show any extrafollicular follicular dendritic cell (FDC) expansion (inset); a clonal B‐cell population in a cervical LN biopsy was detected by polymerase chain reaction with the BIOMED‐2 assay (IGH FR3‐JH) (right). B, A groin LN showing typical features of AITL. Upper panels: on an H&E‐stained section (left) there is striking high endothelial venule (HEV) hyperplasia, amidst which is an infiltrate of medium‐sized atypical lymphoid cells in a background of histiocytes, plasma cells, and eosinophils. On a CD21‐stained section (right), there is prominent FDC expansion, seen to encircle HEVs. Lower panels: the atypical lymphoid cells are strongly positive for PD1 (left), and a proportion are positive for CD10 (left side of the right panel) and CXCL13 (right side of the right panel).