Cumulative family tree for spontaneous primary lymphomas. Lymphoma families were evaluated over multiple generations for their sensitivity to CD20 mAb as in Figure 4. Lymphomas isolated from either CD20 mAb-treated mice (bold text) or control mAb-treated mice (plain text) were either resistant (red) or sensitive (blue) to CD20 immunotherapy. Bracketed numbers indicate lymphoma sensitivity to CD20 immunotherapy. A total of 167 lymphomas have been isolated, including the following: primary (n = 22), secondary (n = 34), tertiary (n = 45), quaternary (n = 38), quinary (n = 18), senary (n = 7), and septenary (n = 3) generations within families. Asterisks indicate specific lymphomas analyzed as in Figures 1-6 (n = 53).