KRAS and neoplasm: Cell lines established from urethane-induced tumours grew poorlyin vitro and failed to grow when transplanted into mice,probably as urethane-induced tumours are typically very low grade and often onlypossess a mutation in Kras (Q61R), lacking any further oncogenic alterations.However, a number of cell lines were readily established from KPA and KPARautochthonous tumours and single-cell cloned.