N-ethyl-N-nitrosourea (ENU)–induced mutagenesis accelerated tumorigenesis in MN1-TEL–expressing mice.MN1-TEL/Mx1-Cre mice (6 to 8 weeks old) were injected with ENU 10 days after treatment of the mice with pI-pC (n = 21) or PBS (n = 19). (B) Expression of T-lymphoid tumor-related genes in MN1-TEL–positive T-lymphoid tumors. Quantitative RT-PCR results are shown. The value normalized to β-actin in each sample was compared with that of a reference sample (another normal tissue, set as 1) to determine the relative expression level. C indicates control MN1-TEL/Mx1-Cre thymocytes without pI-pC (n = 5); T, tumors (n = 5).