Prognostic significance of Bax protein expression in diffuse aggressive non-Hodgkin's lymphoma

Bax is a proapoptotic member of the Bcl-2 protein family. The incidence and prognostic significance of Bax protein expression in diffuse non-Hodgkin's lymphomas with a large cell component (DLCL) was determined by an immunohistochemical method by using paraffin-embedded tumors from a cohort of patients treated uniformly with combination chemotherapy (n = 139). All patients were between 16 and 70 years of age and had advanced stage disease of diffuse large cell type (diffuse mixed, diffuse large cell, immunoblastic, or anaplastic large cell). Paraffin sections from diagnostic biopsies were successfully immunostained for Bax in 113 cases. Of these, 7 (6%) tumors were scored as Bax immunonegative (< 1% Bax-stained tumor cells), 42 (37%) as low (1% to 10%), 9 (8%) as low-intermediate (11% to 30%), 25 (22%) as high-intermediate (31% to 70%), and 30 specimens (27%) as high for Bax expression (> 70%). Of the 7 Bax-immunonegative lymphomas, all also scored low (< or = 10% immunostained tumor cells) for Bcl-2 expression, whereas 78 of the 106 (74%) Bax-immunopositive tumors had low Bcl-2 expression. By itself, Bax expression was not of prognostic significance in univariate analysis, although there was a clear trend for patients with Bax-immunonegative lymphomas (n = 7) to relapse sooner and to die faster than patients whose tumors contained Bax-immunopositive malignant cells (n = 106; 8-year overall survival 29% versus 55%; P = .06). When combined with Bcl-2 immunostaining data, Bax provided additional prognostic information. Among patients with Bcl-2 low-expressing DLCLs, for example, Bax immunonegativity was associated with lower 8-year relapse-free survival (RFS; 29% v 61%; P < .01) and lower 8-year overall survival (OS; 29% v 63%; P < .05), suggesting that absence of Bax protein connotes a more aggressive phenotype when Bcl-2 protein is also not expressed at high levels. In contrast, low Bax expression was associated with improved 8-year disease-free survival (52% v 16%; P < .02), RFS (47% v 11%; P < .02), and OS (64% v 11%; P < .01) in patients whose tumors expressed Bcl-2 at high levels, suggesting that the combination of high levels of Bax and Bcl-2 expression is more deleterious than high levels of Bcl-2 expression alone. Bax expression failed to provide additional prognostic information beyond Bcl-2 expression in multivariate analysis that included the clinical International Prognostic Index factors (age, stage, lactate dehydrogenase, performance status, and number of extranodal sites) and immunophenotype. Taken together, the results suggest that Bax expression is not a major prognostic marker in DLCL. However, the interactions of the Bcl-2 and Bax expression data with respect to clinical outcome may shed new insights into the biological significance of Bcl-2/Bax protein heterodimerization.