For safety reasons, the first patients treated in the study will receive a low dose of gemcitabine. If that dose does not cause severe side effects, the next group will receive a higher dose of gemcitabine than given to the earlier group, or may receive a lower dose if side effects occur. In addition, the first three patients treated on this study will receive the gemcitabine once weekly. If this is tolerated, subsequent patients will receive the medication twice weekly.