Histopathology and recurrent SNVs in IVLBCL. (A) H&E-stained section of the pituitary from case no. 4, which had a RAC2 switch 2 domain mutation p. R68Q (NM 002872.5) (×20 original magnification shows large, atypical lymphocytes within sized vessels). (B) High-power H&E image showing large, atypical lymphocytes within the vascular lumen (×100 original magnification). (C) A CD20 immunostain demonstrates large intravascular B cells (×20 original magnification). (D) A CD34 immunostain confirms that large cells are confined to the vascular lumen (×60 original magnification). (E) Oncoplot²⁴ showing top cooccurring mutations detected in 6 patients with IVLBCL. Horizontal lines represent genes, and the vertical line indicates a single patient. The type of mutations is color-coded in the legend. Mean variant allele frequency for each gene is depicted in the bar plot on the left-hand side. The tumor mutation burden (TMB) for each patient is represented on the upper side of the plot. H&E, hematoxylin and eosin.