For instance, a heterotypic spheroid model (combined of pheochromocytoma cells and primary cancer-associated fibroblasts (CAFs)) was used to test the differential response of wild-type and SDHB/SDHD knock-down pheochromocytoma cells to the pro-migratory factors released by CAFs.59 To be noted, the 3D heterotypic spheroids displayed increased tumorigenic potential in terms of migratory capabilities compared to that of 3D homotypic cancer spheroids. The gene discussed is SDHD; the disease is hereditary pheochromocytoma-paraganglioma.