Lymphomas and leukemias in mice.

Lymphomas are among the most common tumors in many strains and stocks of mice, especially those used in safety assessment. CD-1, C57BL/6, B6C3F1 and B6;129 mice develop 10-50% incidences of lymphomas in aging mice. Most of the tumors are B-cell lymphomas of the follicular type, arising in spleen, mesenteric lymph node and/or Peyer's patches. Lymphomas and leukemias may be induced by chemicals, retroviruses and irradiation. Genetics also play a major role in mouse lymphomagenesis and leukemogenesis. The most potent chemical carcinogens require only a single injection in young mice to induce a high incidence of lymphomas, often thymic T-cell lymphoblastic lymphomas. Several genetically engineered mouse lines have high incidences of these tumors. In 2-year carcinogenesis bioassays, increases of incidences of B-cell lymphomas (which occur naturally in controls) are indicative of less potent carcinogens. Classifications of the lymphomas and leukemias have evolved over the years. The practical WHO toxicologic pathology lymphoma and leukemia classification was developed by collaboration between the US STP, RITA, BSTP and JSTP. A more recent mouse lymphoma and leukemia classification was published by a committee of the US NCI Mouse Models of Human Cancers Consortium. This classification follows closely the more detailed human WHO classification and can be used for mouse models of lymphoma and leukemia.