MAP3K21 and metastatic neoplasm: Priestley et al. characterised 2520 samples of metastatic tumours from 22 solid cancer types.24 Consistent with other results, they found no evidence of driver mutations that were specific to metastases,24 but they did find alterations in the MLK4 gene (which encodes mixed lineage kinase 4) frequently associated with metastatic tumours.