Thyroid Stem Cells and Cancer.pdf

ORIGINAL STUDIES, REVIEWS, AND SCHOLARLY DIALOG FRONTIERS IN THYROID CANCER Thyroid Stem Cells and Cancer Thomas Klonisch,1,2 Cuong Hoang-Vu,3 and Sabine Hombach-Klonisch1,4 Background: Thyroid gland development and function are essential for life, and recent findings indicate the presence of stem=progenitor cells within the thyroid gland as a potential source of tissue regeneration and cancer formation. Summary: This review summarizes the current knowledge on early differentiation of thyroid cells from embryonic stem cells and highlights exciting concepts and recent novel findings on adult thyroid stem=progenitor cells in the normal thyroid gland and in thyroid cancer. Other potential sources and markers of stem=progenitor cells in the thyroid include bone marrow, microchimerism, and embryological remnant-derived multifocal solid cell nests. Finally, we discuss new therapeutic strategies that target thyroid cancer stem cells. Conclusions: Thyroid stem=progenitor cell populations are present in the normal and diseased thyroid gland. Advances in normal and cancer thyroid stem cell biology will be essential for future targeted therapies. Introduction Stem cells are pluripotent, clonogenic, and self-renewing, show plasticity to differentiate into cell types of a particular tissue they reside in, and often transdifferentiate (1). These qualities and the capacity of stem cells for tissue renewal and damage repair make them attractive targets (2). However, the combination of mutations affecting stem cell differentiation potential and unlimited growth potential may generate cancer stem cells (CSCs). Specific stem cell popula- tions have been identified in numerous normal and diseased organs and tissues (3,4). Thyroid cancer is the most common carcinoma of endo- crine glands, comprising *1% of all malignancies, with a 3:1 female=male ratio, and North America has one of the highest incidences of this cancer among all malignancies (5,6). Four types of thyroid carcinoma, namel