p21/WAF1 Cyclin-Kinase Inhibitor Expression in Non-Hodgkin's Lymphomas: A Potential Marker of p53 Tumor-Suppressor Gene Function

p21WAF1 (wild-type p53-activated fragment 1} is involved in the control of mammalian cell cycle through the binding and inhibition of cyclin-dependent kinases (Cdk). Because the product of WAF1 gene is a potent downstream effector of the p53 tumor-suppressor gene function, its pattern of cellular expression might correlate with nuclear accumulation of p53-encoded protein and/or p53 gene mutations occurring in malignant lymphomas. To investigate this issue, we analyzed immunohistochemically the expression of p53 and p21WAF1 proteins in tissue involved by non-Hodgkin's lymphomas (NHLs; 253 cases) of various histologic types. In a proportion of them (80 cases), we also investigated the possible presence of p53 gene mutations using single-strand conformation polymorphism analysis and direct DNA sequencing. The absence of both p21WAF1 and p53 proteins was observed in 147 of 217 cases (67.7%) among CD30 NHL and in only 8 of 36 (22.2%) CD30+ cases, which were mostly anaplastic large-cell lymphomas. A consistent number (>10%) of p21WAF1-expressing cells was shown in 48 of 253 (18.9%) NHL cases, with a higher incidence in CD30+ cases (25/36 [69.4%]), which mostly (21/36) coexpressed p53. These latter cases were characterized by a germline configuration of the p53 gene. In 50 of 253 NHL samples (19.7%), 47 of which (21.6%) belong to the CD30 group, neoplastic cells were p53+/p21-. In all of these cases, the p53+ cells accounted for more than 50% of neoplastic cells, up to 100%. Point mutations of p53 gene were solely observed in all investigated cases with this latter phenotype. Our findings strongly suggest that the combined immunohistochemical evaluation of p53 and p21WAF1 is a valuable means of assessing the functional status of the p53 tumor-suppressor gene product in NHL with potential application in the monitorage and prognostication of individual cases.