Issues and epidemiological evidence regarding radiation-induced thyroid cancer.

The available information on the induction of thyroid cancer in humans by ionizing radiation is summarized and weaknesses or gaps in assessing risk are identified. Issues to be addressed include: average estimates of thyroid cancer risk from external irradiation, the effects of age on thyroid cancer induction, shape of the dose-response curve for acute irradiation, magnitude of risk at low doses, effects of dose fractionation or dose protraction, the relative effectiveness of iodine-131 (131I) in inducing thyroid cancer compared to external radiation, the temporal course of radiogenic thyroid cancer risk, mortality caused by thyroid cancer, host-susceptibility factors for radiogenic thyroid cancer, and biological factors in risk. It is concluded that the most important needs are to obtain more information on thyroid cancer risks following low-level or highly fractionated radiation exposures and following 131I exposure in children.     

Cardiac stem cells: translation to human studies

The discovery of multiple classes of cardiac progenitor cells in the adult mammalian heart has generated hope for their use as a therapeutic in heart failure. However, successful results from animal models have not always yielded similar findings in human studies. Recent Phase I/II trials of c-Kit (SCIPIO) and cardiosphere-based (CADUCEUS) cardiac progenitor cells have demonstrated safety and some therapeutic efficacy. Gaps remain in our understanding of the origins, function and relationships between the different progenitor cell families, many of which are heterogeneous populations with overlapping definitions. Another challenge lies in the limitations of small animal models in replicating the human heart. Cryopreserved human cardiac tissue provides a readily available source of cardiac progenitor cells and may help address these questions. We review important findings and relative unknowns of the main classes of cardiac progenitor cells, highlighting differences between animal and human studies