Summary
The reason for this study is to see if the study drug selpercatinib is safe and more
effective compared to a standard treatment in participants with rearranged during
transfection (RET)-mutant medullary thyroid cancer (MTC) that cannot be removed by
surgery or has spread to other parts of the body. Participants who are assigned to the
standard treatment and discontinue due to progressive disease have the option to
potentially crossover to selpercatinib.