Although the inherently greater chemo- and radio-sensitivity of EL4 lymphoma, which is reflected in its brisk and presumably P53-mediated apoptosis [35], may help to explain EL4 tumor eradication by the combination of chemotherapy and low doses of La-directed radioimmunotherapy, other factors may account for the reduced and differential sensitivity to this combination treatment of the carcinoma cell lines, LL2, in particular. This evidence concerns the gene TP53 and lymphoma.