Expression and prognostic effect of CD37 antigen in patients with DLBCL. (A-B) Representative CD37⁻ and CD37⁺ (red) IHC results (×60). Cell nuclei were counterstained with hematoxylin (blue). Images were obtained with an Olympus AX70 microscope with a DP71 camera. (C) Histogram of CD37 IHC scores in the DLBCL discovery cohort. (D) A scatter plot for CD37 expression in DLBCL and comparison between GCB and ABC cell of origin. (E) Patients with CD37⁻ DLBCL had significantly worse OS and PFS compared with patients with CD37⁺ DLBCL, with a HR of 2.80 and 95% CI of 1.95 to 3.38 for OS, and a HR of 2.89 and 95% CI of 2.07 to 3.45 for PFS. (F-H) The adverse prognostic effect of CD37 loss was independent of GCB and ABC cell of origin, high and low IPI scores, and primary nodal (NL) and primary extranodal (ENL) origin.