Alternatively, if the causal link between irradiation and tumorigenesis from p53−/− cells does not involve the selection of radioresistant p53 null cells, and instead completely relies on the mutagenic action of irradiation, then irradiation should enhance development of T-cell lymphomas in mice with non-chimeric p53−/− hematopoietic systems. The gene discussed is TP53; the disease is T-cell non-Hodgkin lymphoma.