The sample size in other studies was generally small and ranged from N = 5 patients with metastatic PCC of a cohort of N = 57 with PPGL [31], N = 10 with metastatic PPGL [30], N = 17 with SDHx (N = 13) and MEN2a (N = 4)-associated metastatic PPGL [33] to an unknown number of N = 27 patients with recurrent or metastatic PPGL among N = 36 patients with PPGL [32]. This evidence concerns the gene RET and adrenal gland pheochromocytoma.