Characteristics of lymphomas in the BALB/cfRIII mouse strain

The occurrence of 392 lymphomas in 1607 BALB/cfRIII mice from F0 to F45 is analyzed. Lymphoma incidence increased rapidly in the first 5 generations, reached a high plateau from F6 to F20 and then decreased slowly until it disappeared altogether. After F35, only sporadic cases of lymphoma have been observed. The morphologic characteristics of 350 of these lymphomas observed from F0 to F20 are described. Three main types of lymphomas have been recognized on the basis of gross morphology, histology and age: a) early, lymphocytic, with thymic involvement; b) early, lymphocytic, without thymic involvement; and c) late, histiocytic, without thymic involvement. The first 2 types are virus-induced and thymus-dependent, and the third type is both virus and thymus independent. Lymphomas without thymic involvement and histiocytic lymphomas increased with the generations. The source of causative virus, the interference with mammary tumors, and the possible cell types of origin of lymphomas are discussed.