Microbial impact on tumorigenesis of heritable cancers proximal to the gut is well-documented. Whether the microbiota influences cancers arising from inborn mutations at sites distal to the gut is undetermined. Using two models of heritable cancer, Trp53-deficient mice and Wnt1-transgenic mice, and a gnotobiotic approach, we found the microbiota to be inconsequential for tumor development. This work furthers our understanding of the degree of the microbial impact on tumor development.