Lapatinib, being a small molecule TKI, seems to penetrate more readily into the CNS, as illustrated by pre-clinical data that showed in vitro inhibition of phosphorylation of EGFR, HER2, downstream signalling proteins and cell proliferation in brain-seeking breast cancer cell lines MDA-MB-231-BR (with and without HER2), and a corresponding 50–53% reduction in the number of brain metastases developed by nude mice injected with these cells when treated with lapatinib, compared with a control group (Gril et al, 2008). The gene discussed is ERBB2; the disease is breast cancer.