p16 immunohistochemistry in LGFCL, progressed DLCL, and de novo DLCL. (A) LGFCL (case no. 7) showing strong nuclear reactivity (brown nuclear staining) in the majority of the neoplastic follicular center cells (original magnification × 100). (B) Progressed DLCL showing lack of p16 expression in the neoplastic cells (case no. 7). Note the positive (brown) staining in the (internal control) renal tubular epithelial cells (original magnification × 400). (C) De novo DLCL showing diffuse positive staining for p16 in majority of the tumor cells (original magnification × 200). Double immunostaining for p16 and CD20. (D) LGFCL (case no. 5) showing dual reactivity for p16 (brown nuclear stain) as well as strong membrane reactivity for CD20 (red) (original magnification × 100). (E) Higher magnification of (D) (original magnification × 200). (F) Progressed DLCL (case no. 5) showing the absence of p16 expression in the nuclei of the neoplastic CD20⁺ cells. Note the strong p16 expression in the (internal control) endothelial cells (original magnification × 400).