Alternatively, tumor cells can be enriched for brain tumor-initiating cells (BTICs) by sorting for CD133+ cells (35), grown as an adherent layer (31, 36–44), transplanted in the thalamus or subcutaneously to expand the tumor cells (32, 40, 45, 46), or injected intracranially after serial transplantation (16, 35, 40, 46–55). The gene discussed is PROM1; the disease is neoplasm.