In summary, we show that hCAP18/LL-37 is highly upregulated in breast cancer correlating with the expression of ERBB2. In vitro, we also show that they are functionally connected, in that hCAP18/LL-37 amplifies MAPK signalling through ErbB2 and that treatment with LL-37 peptide alters the growth phenotype and stimulates the migration of breast cancer cells. The gene discussed is CAMP; the disease is breast cancer.