Expression of OCT4 and SALL4 in diffuse large B-cell lymphoma

OCT4 and SALL4 are transcription factors within a complex network that functions to maintain pluripotency in primitive stem cells and germ cells. Nuclear expression of OCT4 is widely cited as sensitive and specific for primary and metastatic germ cell tumors and is commonly used in the diagnosis of central nervous system (CNS) germinomas. Studies have failed to systematically examine the expression of OCT4 or SALL4 in diffuse large B-cell lymphoma (DLBCL), although this entity enters the morphologic differential diagnosis of some germ cell tumors. A retrospective review was conducted on 145 consecutive cases of DLBCL and testicular lymphoma to evaluate the prevalence of OCT4 and SALL4 expression. Nuclear OCT4 expression was present in 2/11 (18%) testicular DLBCLs and 6/134 (4.5%) nontesticular DLBCLs. Most OCT4⁺ cases demonstrated moderate to strong expression in >50% of neoplastic cells. Rare, weak nuclear SALL4 expression was detected in only 3 nontesticular DLBCLs. Within the extratesticular DLBCL group, 2/6 (33%) primary CNS DLBCLs expressed nuclear OCT4. In addition, OCT4⁺ DLBCL showed an overall predilection toward non-germinal center B-cell phenotype (7/8; 88%) and had a higher than expected rate of CD5 coexpression (4/8, 50%). These results are cautionary against using OCT4 as a sole marker of germ cell differentiation in testicular and extratesticular sites, especially in the CNS. The apparent associations of OCT4 expression with primary CNS DLBCL, non-germinal center B-cell phenotype, and CD5 coexpression raise the question of whether OCT4 expression in DLBCL may reflect more aggressive biology.