Penfluridol, a first-generation antipsychotic agent, has been shown to induce apoptosis in several triple-negative breast cancer (TNBC) cell lines, and in three different in vivo tumour models, including two models of metastases to the brain, where the presence of the blood–brain barrier limits the effectiveness of many conventional chemotherapies. Further analyses revealed reduced integrin β4 expression, suggesting that the antitumour effects of penfluridol occur through inhibition of integrin signalling.