PROM1 and neoplasm: Subsequent studies were focused to characterize CD133+ cells from primary human hepatocarcinomas, providing evidence that in primary tumor samples these cells account for 1.3 to 13.6% of the total tumor cell population, possess the capacity to form tumor spheroids composed by undifferentiated tumor cells and have a greater ability to form tumors of identical morphology compared to the parental tumors, when inoculated into immunodeficient mice [109].