Tracing the cellular origin of cancer.

Although many genes that lead to different types of cancer when mutated have been identified, the cells that initiate tumour formation following accumulation of these mutations have, until recently, remained elusive. This review explores how mouse genetic lineage-tracing experiments that allow the expression of oncogenes and/or the deletion of tumour suppressor genes in defined cell lineages have been instrumental in defining the cellular origin of different solid tumours in mouse models for various human cancers.