Frequent alteration of MDM2 and p53 in the molecular progression of recurring non-Hodgkin's lymphoma.

AIMS: Recurrence of non-Hodgkin's lymphoma with or without transformation is often associated with increased clinical drug resistance and poor prognosis indicating molecular progression. The study addresses the currently poorly understood molecular mechanisms underlying relapsing non-Hodgkin's lymphoma. METHODS AND
RESULTS: We have analysed sequential biopsies from 42 non-Hodgkin's lymphoma patients immunohistochemically for p53 alterations (based on p53 and p21Waf1 expression), as well as for expression of MDM2, p27Kip1 and cyclin D3. Relapse of follicle centre lymphoma was associated with p53 alterations as 5/6 (83%) follicle centre lymphomas with normal p53 at diagnosis showed p53 alterations at relapse. Of these cases, three showed transformation to diffuse large B-cell lymphoma. p53 alteration was also associated with relapse of de novo diffuse large B-cell lymphoma and T-cell non-Hodgkin's lymphoma, as 2/5 (40%) diffuse large B-cell lymphomas and 3/9 (33%) T-cell non-Hodgkin's lymphomas with normal p53 at diagnosis showed p53 alterations at relapse. No indolent non-Hodgkin's lymphoma case showed MDM2 over-expression at diagnosis, whereas 4/5 (80%) transformed diffuse large B-cell lymphomas developed MDM2 over-expression.
CONCLUSION: Our data are consistent with the notion that p53 alterations are important for the histological transformation of follicle centre lymphoma. However, the data also suggest that relapsing follicle centre lymphomas without overt transformation often have p53 alterations and increased risk of transformation, and that relapse of de novo diffuse large B-cell lymphomas and T-cell non-Hodgkin's lymphomas is associated with p53 alterations. Furthermore, our results are consistent with an association of MDM2 over-expression with histological transformation of both follicle centre lymphoma and marginal zone B-cell lymphoma.