B[a]P, given three times a week by oral gavage for 13 weeks at 4.3, 13, or 39 mg/kg body weight resulted in a dose-dependent increase in lymphomas, with up to a 90% incidence in Eμ-Pim1 mice during the observation period of 40 weeks; in contrast, the non-transgenic mice did not develop lymphomas. The gene discussed is PIM1; the disease is lymphoma.