Cancer modifier loci are genetic loci characterized by allele-specific effects on cancer development, e.g., stimulation or inhibition of tumor development and/or tumor size/progression. Cancer modifier loci may comprise a “null” allele, with no effects on tumor phenotypes, and a “susceptibility” or “resistance” allele, which affects tumor phenotype in a dominant, codominant, or recessive way.
Evidence for the existence of cancer modifier loci came first from studies in rodent models. Indeed, several studies showed that susceptibility to spontaneous and induced tumorigenesis are under genetic control. Crosses between cancer-susceptible and cancer-resistant strains may result in F1 hybrids either susceptible or resistant to tumor formation, depending on which of the two alleles (susceptibility/resistance) is dominant in the cross.
In humans, evidence for the...