PROM1 and familial pancreatic carcinoma: To test if these CSCs originated from dedifferentiation of CD133− cancer cells, we cocultured lethally irradiated pancreatic cancer cells (20 Gy, lethal dose optimized in Fig. S1B) or nonirradiated control cells (0 Gy) together with sorted CD133– cancer cells using a Millicell insert system.