There are some arguments for promoting the use of 131I-mIBG therapy at an earlier stage: (1) due to disease progression, including tumor cell dedifferentiation, loss of specific neurotransmitter transporters, and gene expression, mIBG does not accumulate in parts of PPGL lesions19–24; and (2) sometimes, refractory PPGLs rapidly progress within a few months or years after initial diagnosis. Here, SLC6A2 is linked to neoplasm.