When lower doses of tamoxifen were administered (1–10 μg), to activate oncogenic K-ras in fewer cells, thymic lymphomas (Figure 4A) and pulmonary adenocarcinomas (Figure 4B) were observed in 100% of the K-ras mice within 14–40 weeks post-treatment (7/7 of 10 μg-dosed mice and 5/5 of 1 μg-dosed mice) but never in the tamoxifen-treated K-ras+/+ controls (0/10). The gene discussed is KRAS; the disease is thymus lymphoma.