Agents that are showing promising results in early phases of clinical trials include betulinic acid; hedgehog signaling pathway inhibitors, such as cyclopamine and GDC-0449; alpha-melanocyte-stimulating hormone analogs, such as afamelanotide; epidermal growth factor receptor inhibitors, such as gefitinib and erlotinib; anti-epidermal growth factor receptor monoclonal antibodies, such as cetuximab and panitumumab; and the 5-fluorouracil prodrug capecitabine.