Conditional mouse models of sporadic cancer.

First-generation mouse tumour models, which used transgenic mice or conventional knockouts, are now being superseded by models that are based on conditional knockouts and mice that carry regulatable oncogenes. In these mice, somatic mutations can be induced in a tissue-specific and time-controlled fashion, which more faithfully mimics sporadic tumour formation. These second-generation models provide exciting new opportunities to gain insight into the contribution of known and unknown genes in the initiation, progression and treatment of cancer, and mimic human cancer better than ever before.