Expression of p21 Protein Predicts Clinical Outcome in DLBCL Patients Older than 60 Years Treated with R-CHOP but not CHOP: A Prospective ECOG and Southwest Oncology Group Correlative Study on E4494

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To prospectively investigate the prognostic significance of p21 and p53 expression in diffuse large B-cell lymphoma in the context of the U.S. Intergroup trial comparing conventional cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy to rituximab-CHOP (R-CHOP) induction, with or without maintenance rituximab. Immunohistochemical staining of 197 paraffin-embedded biopsy specimens was scored by an independent panel of experts. The cyclin-dependent kinase inhibitor, p21, was expressed in 55% of cases examined. In a multivariable analysis adjusting for International Prognostic Index score and BCL2 status, p21 expression was a significant, independent, favorable predictive factor for failure-free survival (relative risk, 0.3; P = 0.001) and overall survival (relative risk, 0.3; P = 0.003) for patients treated with R-CHOP. Expression of p21 was not predictive of outcome for CHOP-treated patients. Only p21-positive cases benefited from the addition of rituximab to CHOP. Among p21-positive patients, treatment with R-CHOP was associated with a higher failure-free survival rate at 5 years compared with CHOP (61% versus 24%; P = 0.01). In contrast, no significant differences were detected in failure-free survival according to treatment arm for p21-negative patients. Expression of p53, alone or in combination with p21, did not predict for outcome in univariable or multivariable analyses. In this study, p21 protein expression emerged as an important independent predictor of a favorable clinical outcome when rituximab was added to CHOP therapy. These data suggest that rituximab-related effects on lymphoma survival pathways may be functionally linked to p21 activity.