If participant is found to be eligible to take part in this study, they will be assigned to a dose level and schedule of sorafenib based on when they joined this study. Up to 5 dose levels and schedules will be tested. Three (3) participants will be enrolled at each dose level for Phase I of the study. The first group of participants will receive dose level "0" of sorafenib. If unacceptable side effects are seen, a dose lower than level "0" will be tried. If no side effects are seen, the next group of 3 participants will be placed on a higher dose level, called Level "1." Each new group will either receive a higher or lower dose of sorafenib or take it more or less often than the group before it, based on whether intolerable side effects are seen. This will continue until the best tolerable dose and schedule of sorafenib is found. Once the best tolerable dose and/or schedule is found, the last 10 participants will be enrolled and will take sorafenib at that dose and schedule. This last group of 10 is considered the early Phase II part of the study.