CD137L^−/− and CD27;CD137L^−/− mice are predisposed to develop B-cell lymphoma. WT, CD137L^−/− and CD27;CD137L^−/− mice of various ages (6-16 months) were killed and examined blindly for indications of lymphoma according to Bethesda proposals.²⁷  (A) For each genotype frequencies of lymphoma incidence were determined per age in months. The risk to develop lymphoma was determined on the basis of locally weighed polynomial regression. (B) Trend lines for the smoothed estimates were calculated to determine the lymphoma incidence probability for each genotype. Diagnosis of lymphomas is presented in Table 2.