Since these Rint1+/- mice were on a highly mixed 129 x B6 genetic background, which is known to have a high incidence of spontaneous lymphoma development[16], we cannot exclude the possibility that at least some of the tumor predisposition in Rint1+/- mice observed in Lin et al is attributable to genetic background rather than the Rint1 knockout allele. This evidence concerns the gene RINT1 and lymphoma.