Frequent disruption of the RB1 pathway in diffuse large B cell lymphoma: prognostic significance of E2F-1 and p16(INK4A)

In the present study, we analysed 34 de novo diffuse large B cell lymphoma (DLCL) from a population-based lymphoma registry for alterations of the RB1 pathway at the genetic (RB1 and CDK4) and protein (pRb, cyclin D1, cyclin D3, CDK4, and E2F-1) level. The results were correlated with the data from our previous studies of CDKN2A deletion and hypermethylation, other p53 pat hway components, p27(Klp1) expression, and proliferation, as well as with c linical outcome, including prognosis. We found aberrant pRb expression in f our (12%) of 34 DLCLs. One of these had a point mutation in intron 3 10 bp downstream of exon 3 generating a novel splice signal. Seven tumours (21%) showed cyclin D3 overexpression, including all three thyroid lymphomas (P = 0.006). Cyclin D3 overexpression and p16(INK4A)/pRb aberrations were mutua lly exclusive, supporting an oncogenic role for cyclin D3 in DLCL, p16(INK4 A) inactivation, cyclin D3 overexpression, or aberrant pRb expression was i dentified in 18 of 34 DLCLs (53%). Combining these results with our previou s p53 pathway studies showed that 82% of the de novo DLCLs had alterations of these pathways, and that both pathways were altered in 13 cases (38%). L ow E2F-1 expression was associated with treatment failure (P = 0.020), and multivariate analysis of overall survival identified both low E2F-1 express ion (relative risk = 6.9; P = 0.0037) and p16(INK4A) inactivation (relative risk = 3.3; P = 0.0247) as independent prognostic markers. These data supp ort a role of E2F-1 as tumour suppressor gene in lymphoma and strongly sugg est that the RBI and p53 pathways are important in the development of de no vo DLCL. Furthermore, low E2F-1 expression and p16(INK4A) inactivation may serve as prognostic markers for patients with this type of lymphoma.