Additional evidence of a claudin 1 tumor suppressor role comes from in vitro studies showing that anti-claudin 1 antibodies promote transformation of MCF‐12A breast epithelial cells [16] and re-expression of claudin 1 induces apoptosis in tridimensional cultures of MDA‐MB‐361 breast cancer cells [17]. The gene discussed is CLDN1; the disease is breast cancer.