Two genetically modified mouse pheochromocytoma (MPC) cell lines, one positive and one negative for hypoxia-inducible factor 2α expression (MPC+HIF-2α and MPC+EV [empty vector], respectively), were X-ray-conditioned through fractionated irradiation at sublethal doses. The gene discussed is EPAS1; the disease is hereditary pheochromocytoma-paraganglioma.