Activation of the NF-kappaB signalling pathway in diffuse large B-cell lymphoma: clinical implications

Aim: To characterize the activation of the nuclear factor (NF)‐κB pathway in diffuse large B‐cell lymphoma (DLBCL) by immunohistochemistry. Methods and results: Sixty‐six DLBCLs treated with anthracycline‐containing chemotherapy were evaluated with antibodies against phosphorylated p65 (P‐p65), p65, p50, p52, IKKα, and phosphorylated IκB (P‐IκB). NF‐κB activation was based on the expression of P‐p65, P‐IκB, and nuclear expression of p65 or p52 in the tumour cells. P‐p65 and P‐IκB were expressed in 13 (20%) and 17 cases (26%), respectively. p65, p52 and IKKα were found in the cytoplasm. A correlation was found between expression of P‐p65 and P‐IκB (P < 0.0001), but not between the two subtypes of DLBCL germinal centre B cell and non‐germinal centre (GC)]. P‐p65+ tumours showed a better response to chemotherapy (P = 0.025) and a trend to increased event‐free survival (P = 0.08). However, P‐IκB expression was not associated with either clinical response or survival. Bcl‐2 was not preferentially expressed on DLBCL tumours with NF‐κB activation, as determined by expression of P‐p65 and P‐IκB proteins. Conclusions: NF‐κB activation in DLBCL is preferentially mediated through the classical pathway and a novel mechanism involving phosphorylation of p65. Activation of NF‐κB by P‐p65 is associated with good prognosis. NF‐κB activation is not confined to non‐GC DLBCL exclusively.