Gemcitabine, an inhibitor of DNA synthesis, is currently in small phase 2 studies of HL. It has shown limited results and is proposed to be used as a combination drug. The semisynthetic vinca alkaloid vinorelbine, a more selective therapy than other available drugs, has had response rates as high as 50% in patients with relapsed or refractory HL, although the number of patients studied has been limited to 32. Several other drugs are also being investigated in small studies in the US and Germany.