Expression of signal transducer and activator of transcription 3 (STAT3) in primary central nervous system diffuse large B-cell lymphoma: a retrospective analysis of 17 cases

Most primary central nervous system lymphomas (PCNSL) occurring in immunocompetent patients are diffuse large B-cell lymphomas (DLBCL), characterized by poor prognosis. An activated B-cell (ABC) origin of PCNSL has been postulated based on bcl-6 and MUM-1 expression by majority of these tumors. ABC DLBCL has been functionally subdivided using gene expression profiling and immunohistochemical analysis into STAT3-high and STAT-3 low subsets. A potentially crucial difference between STAT3-high and STAT3-low ABC DLBCL is in the expression of bcl-2 family members. STAT3-high cases are generally bcl-2 low and STAT3-low cases show higher expression of bcl-2. Further mechanisms such as activation of nuclear factor-kappa B (NF-κB) activation seem to be responsible for upregulation of bcl-2 in ABC subtype of DLBCL with an adverse outcome. As deregulation of STAT-3 pathway is known to play a critical role in ABC DLBCL and majority of the PCNSL are of the ABC subtype we studied the immunohistochemical expression of STAT-3 proteins in PCNSL along with other traditional markers (CD10, bcl-6, MUM-1 and bcl-2) in 17 cases of PCNSL occurring in immunocompetent patients. Despite lack of STAT3 expression in all our cases, majority (70%) of the patients with bcl-2 positive PCNSL had an adverse outcome similar to that reported in systemic lymphomas of ABC subtype. Based on our observations we propose that PCNSL represents a distinct subset of ABC diffuse large B-cell lymphomas with low STAT3 expression and perhaps mechanisms other than interaction of STAT-3 and NF-κB pathways may play a role in upregulation of bcl-2 in PCNSL. To the best of our knowledge expression of STAT-3 protein in PCNSL which represents a distinct anatomical subset of ABC DLBCL with a dismal prognosis has not been studied before.