
Family trees of lung cancer cells, built using CRISPR-based lineage tracing, reveal in depth how cancer evolves from its earliest stages to become aggressive and capable of spreading throughout the body. Over time, cancer cells can evolve to become resistant to treatment, more aggressive, and metastatic—capable of spreading to additional sites in the body and forming new tumors. The more of these traits that a cancer evolves, the deadlier it becomes. Researchers want to understand how cancers evolve these traits in order to prevent and treat deadly cancers, but by the time cancer is discovered in a patient, it has typically existed for years or even decades. The key evolutionary moments have come and gone unobserved.