Early trials have shown that antibody-drug conjugates (ADCs) directed to targets found in secondary brain cancer have therapeutic efficacy.246 For example, trastuzumab emtansine, an anti-HER2 (also known as ERBB2, a member of the EGFR RTK family) ADC, has shown promising anti-tumour activity in breast cancer metastasis to the brain (recently reviewed ref. 246). Here, ERBB2 is linked to breast cancer.