INTS13 and neoplasm: The GC tumor-resistant phenotype of Line 4-T females provided two key findings in support of the chosen congenic mapping strategy to resolve Gct1: (1) confirmation that the transferred genomic segment from the CAST strain encompassed the Gct1 locus, such that the Gct1SW tumor susceptibility alleles were replaced by Gct1CA resistance alleles, and (2) confirmation that Gct1SW is the driver for the ovarian GC tumor susceptibility phenotype, despite the accumulated genetic evidence for multiple genetic modifiers of susceptibility on Chr X and several autosomes.