It was stopped early because a particular breed of rats, (Fischer 344 rats), which are genetically engineered to get bone cancer, got bone cancer, and some of the scientists thought they got it sooner than expected.
Lamiswa kwangoko ngenxa yokuba uhlobo oluthile lwempuku, (iimpuku eziziFischer 344), ezilungiselelwe ngokwemfuza yazo ukuba zifumane umhlaza wamathambo zawufumana kwangoko lo mhlaza zaza ezinye iinzululwazi zacingela ukuba ziwufumene kwangoko kunoko bekulindelekile.