The present invention provides agents for inhibiting the proliferation of cancer cells, wherein the agent inhibits the biological activity of hCAP18/LL-37. In a preferred embodiment, the agent alters the transcription, translation and/or binding properties of hCAP18/LL-37. Preferably, the agent is selected from the group consisting of short interfering RNA (siRNA) molecules, antisense oligonucleotides and compounds with binding affinity for hCAP18/LL-37. The invention further provides methods for inhibiting the proliferation of cancer cells in a patient, as well as methods and kits for diagnosing cancer.