Frequency of the cancer-resistant phenotype in SR/CR mice and the effect of litter seriation.

The SR/CR mouse model of cancer resistance was fortuitously discovered in 1999. It is resistant to a number of different cancer cell lines and the heritable phenotype was demonstrated on different genetic backgrounds. The cancer resistance is transferable to other strains of mice by adoptive transfer of innate immune cells. We independently, for the first time, confirm the findings of the SR/CR phenotype of cancer resistance to the S180 cell line in mice of two different genetic backgrounds: BALB/c and C57BL/6. The SR/CR mice were screened by intraperitoneal injection of S180 cells. The frequency of the SR/CR phenotype in the present study was 30% for the BALB/c strain and 22% for the C57BL/6 strain in the first litters, but the overall frequency was 8% for both strains. A frequency of about 30% was reported in the original US colony. A litter seriation effect on the frequency of the SR/CR phenotype was recorded. The phenotype frequency in the first-born litters was similar to that recorded in the founder colony in the US. There was no significant difference in the frequency of the SR/CR phenotype between the two genders, but the overall frequency of the SR/CR phenotype was significantly higher in litters from SR/CR mice on a BALB/c background compared to litters from SR/CR mice on a C57BL/6 background.