MYCN and neoplasm: Variation in tumor incidence among Th-MYCN mice is influenced by their background strains.11 In our study involving the backcrossed inbred 129+Ter/SvJcl mouse strain, all Th-MYCN homozygote (Th-MYCN+/+) mice succumbed to tumors (data not shown), while approximately 80% of Th-MYCN hemizygote (Th-MYCN+/−) mice succumbed to tumors, with the remaining 20% surviving without sex bias (Figure 1A).