Morphology and immunophenotype of PTNFL. (A) A representative PTNFL showing architectural effacement by follicular proliferation (H&E, ×40). Follicles were composed of medium-sized cells with blastoid features (H&E, ×1000) that were PAX5⁺ CD10⁺ with dim or no BCL2 expression. There were scattered occasional CD3⁺ BCL2⁺ T cells within follicles. Follicles harbored a tight network of CD21⁺ follicular dendritic cell meshworks and had a relatively high proliferation index, on the basis of Ki-67 staining. Magnification: ×100 for PAX5, CD10, BCL2, CD3, CD2; ×200 for Ki-67. (B) FISH for BCL2 rearrangement, using LSI BCL2 Dual color break apart rearrangement probe (left), and FISH for BCL6 rearrangement, using LSI BCL6 Dual color break apart rearrangement probe (right). PTNFLs lacked both BCL2 and BCL6 rearrangements as evidenced by colocalization of probes. (C) LSTFL had significantly lower progression-free survival than PTNFL (P < .001).