In clinical study of 44 GBM patients, the CD133+ tumour cell proportion of ≥ 2% negatively correlated with overall survival.12 Additionally, mRNA expression analyses in GBM patients showed that high sample CD133 mRNA expression was a significant prognostic factor for adverse overall survival.18,19 These opposite results may be related to other treatment protocol (radiochemotherapy), different primary antibody used for CD133 immunohistochemical detection, as well as to the fact that mRNA expression study samples contained up to 50% of non-tumour tissue, which may also have contained CD133.20 The gene discussed is PROM1; the disease is glioblastoma.