Yang et al. BMC Cancer 2010, 10:133 http://www.biomedcentral.com/1471-2407/10/133 mechanism of gene overexpression in human cancers [30]. To determine whether the overexpression of Bmi-1 in ovarian carcinomas was caused by gene amplification, the amplification status of Bmi-1 was examined by FISH. In our 96 informative cases of ovarian carcinomas by both IHC and FISH simultaneously, intensive expres- sion of Bmi-1 was detected in all (8/8) ovarian car- cinomas that had Bmi-1 amplification. However, amplification of Bmi-1 was not observed in 28 other ovarian carcinomas with intensive expression of Bmi-1. These results indicate that the expression level of Bmi-1 protein in ovarian carcinoma does not always coincide with gene amplification. In addtion, in bladder cancers, a significant difference in Bmi-1 protein expression and in mRNA levels was obtained, but Bmi-1 protein was up-regulated to a much greater extent than Bmi-1 mRNA in cancer tissue compared with non-cancerous tissues, implying that the major source of Bmi-1 expres- sion might be dysregulation at the post-transcriptional level in bladder cancers [19]. These data suggest that the up-regulation of protein expression of Bmi-1 in human cancers is complicated and it might be regulated not only by gene amplification, but also by other mole- cular mechanisms including transcriptional regulation and post-translational regulation. Conclusion In summary, in this study, we describe, for the first time, protein expression and amplification patterns of Bmi-1 in normal human ovary, benign, borderline and malignant epithelial ovarian tumor tissues. Our results provide a basis for the concept that increased expression of Bmi-1 in human ovarian carcinoma may be important in the acquisition of an invasive and/or aggressive phe- notype. In addition, our study introduces Bmi-1 expres- sion as a new independent prognostic marker in ovarian carcinoma with intensive expression of Bmi-1 protein in tumor cells predicting poor outcome of the disease for the individual patient. Acknowledgements This study was supported by the grants from the the Major State Basic Research Program of China (2006CB910104), the Nature Science Foundation of China (No.30772334) and Project of Guangdong Science and Technology Agency (No. 2004B35001004 and 2005A30801001). Author details 1State Key Laboratory of Oncology in South China, Cancer Center, Sun Yat- Sen University, No. 651, Dongfeng Road East, 510060 Guangzhou, China. 2Department of Gynecology, the First Affiliated Hospital, Sun Yat-Sen University, No. 78, Zhongshan Road II, 510080 Guangzhou, China. Authors’ contributions GFY evaluated the clinical records and drafted the manuscript. WPH carried out the immunohistochemistry assays and help to draft the manuscript. MYC participated in the statistical analysis and participated in its coordination. HLR performed the immunohistochemical analyses. JHL and Page 8 of 9 HXD help to carry out the immunohistochemistry assays. XYG, MSZ, YXZ and DX participated in the design of the study, in its analysis and in the interpretation of the data. DX designed the study and also participated in evaluated the immunohistochemistry results and wrote the manuscript. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 12 October 2009 Accepted: 8 April 2010 Published: 8 April 2010 References 1. Wingo PA, Ries LA, Rosenberg HM, Miller DS, Edwards BK: Cancer incidence and mortality. 1973-1995, a report card for the U.S. Cancer 1998, 82:1197-207. 2. Freund KM, Dolan NC, Nelson HD: Update in women’s health. Ann Int Med 2003, 138:119-127. 3. DiSaia PJ, Bloss JD: Treatment of ovarian cancer: new strategies. Gynecol Oncol 2003, 90:S24-32. 4. van Lohuizen M, Frasch M, Wientjens E, Berns A: Sequence similarity between the mammalian bmi-1 proto-oncogene and the Drosophila regulatory genes Psc and Su(z)2. Nature 1991, 353:353-355. 5. Haupt Y, Bath ML, Harris AW, Adams JM: Bmi-1 transgene induces lymphomas and collaborates with myc in tumorigenesis. Oncogene 1993, 8:3161-3164. 6. Jacobs JJ, Kieboom K, Marino S, DePinho RA, van Lohuizen M: The oncogene and Polycomb-group gen bmi-1 regulates cell proliferation and senescence through the ink4a locus. Nature 1999, 397:164-168. 7. Lugt NM, Domen van der J, Linder sK, van Roon M, Robanus-Maandag E, te Riele H, Valk M, Deschamps van der J, Sofroniew M, van Lohuizen M: Posterior transformation, neurological abnormalities, and severe hematopoietic defects in mice with a targeted deletion of the bmi-1 pro-oncogene. Genes Dev 1994, 8:757-769. 8. Lessard J, Sauvageau G: Bmi-1 determines the proliferative capacity of normal and leukaemic stem cells. Nature 2003, 423:255-60. 9. Lindstrom MS, Klangby U, Wiman KG: P14ARF homozygous deletion or MDM2 overexpression in Burkitt lymphoma lines carrying wild type p53. Oncogene 2001, 20:2171-7. 10. Bea S, Tort F, Pinyol M, Puig X, Hernandez L, Hernandez S, Fernandez PL, van Lohuizen M, Colomer D, Campo E: Bmi-1 gene amplification and overexpression in hematological malignancies occur mainly in mantle cell lymphomas. Cancer Res 2001, 61:2409-12. 11. Vonlanthen S, Heighway J, Altermatt HJ, Gugger M, Kappeler A, Borner MM, van Lohuizen M, Betticher DC: The bmi-1 oncoprotein is differentially expressed in non-small cell lung cancer and correlates with INK4A-ARF locus expression. Br J Cancer 2001, 84:1372-6. 12. van Kemenade FJ, Raaphorst FM, Blokzijl T, Fieret E, Hamer KM, Satijn DP, Otte AP, Meijer CJ: Coexpression of Bmi-1 and EZH2 polycomb-group proteins is associated with cycling cells and degree of malignancy in B- cell non-Hodgkin lynphoma. Blood 2001, 97:3896-901. 13. Kim JH, Yoon SY, Jeong SH, Kim SY, Moon SK, Joo JH, Lee Y, Choe IS, Kim JW: Overexpression of Bmi-1 oncoprotein correlates with axillary lymph node metastases in invasive ductal breast cancer. Breast 2004, 13:383-388. 14. Kim JH, Yoon SY, Kim CN, Joo JH, Moon SK, Choe IS, Choe YK, Kim JW: The Bmi-1 oncoprotein is overexpressed in human colorectal cancer and correlates with the reduced p16INK4a/p14ARF proteins. Cancer Letters 2004, 203:217-224. 15. Wang H, Pan K, Zhang HK, Weng DS, Zhou J, Li JJ, Huang W, Song HF, Chen MS, Xia JC: Increased polycomb-group oncogene Bmi-1 expression correlates with poor prognosis in hepatocellular carcinoma. Cancer Res Clin Oncol 2008, 134:535-541. 16. Zhang F, Sui L, Xin T: Correlations of Bmi-1 expression and telomerase activity in ovarian cancer tissues. Exp Oncol 2008, 30:70-74. 17. Mihara K, Chowdhury M, Nakaju N, Hidani S, Ihara A, Hyodo H, Yasunaga S, Takihara Y, Kimura A: Bmi-1 is useful as a novel molecular marker for predicting progression of myelodysplastic syndrome and prognosis of the patients. Blood 2006, 107:305-308. 18. Song LB, Zeng MS, Liao WT, Zhang L, Mo HY, Liu WL, Shao JY, Wu QL, Li MZ, Xia YF, Fu LW, Huang WL, Dimri DP, Band V, Zeng YX: Bmi-1 is a