Thyroid cancer is one of the most rapidly increasing
cancers in many countries. Although most
thyroid cancers are differentiated
cancers and easily treated with radioiodine (RI), a portion of differentiated and undifferentiated
cancers is refractory not only to RI
therapy, but also to
radiotherapy and
chemotherapy. Thus, various
alternative therapies have been tested in RI-refractory
thyroid cancers. These
alternative therapies include two major categories: redifferentiation
therapy and recent molecular target
therapy. Several clinical trials have investigated these
therapies. They demonstrated potential effects of the
therapies, although the results have been somewhat limited so far. Thus, the future strategy for undifferentiated
thyroid cancers will involve individualized, lesion-specific, and combined
therapy. In this review, the basic mechanism of each redifferentiation and molecular target
therapy is discussed, and results of recent clinical trials using these therapeutic agents are summarized.