Yang et al. BMC Cancer 2010, 10:133 http://www.biomedcentral.com/1471-2407/10/133 60 (68%) cases showed low expression of Bmi-1, while 28 (32%) cases were observed intensive expression of Bmi-1. Correlation between the expression of Bmi-1 and p16Ink4a and p14ARF in ovarian carcinomas Since it was suggested that modulation of Bmi-1 protein might be involved in human colorectal carcinogenesis by repressing p16Ink4a/p14ARF proteins {14}, we further examined the expression of p16Ink4a/p14ARF by IHC in our ovarian carcinoma cohorts. By utilizing the criterion of a semi-quantitative scale as previously described [14], we found that 36% (64/179) and 17% (30/179) of ovarian carcinomas had negative/down-regu- lated expression of p16Ink4a and p14ARF, respectively. Further correlation analysis demonstrated that no signif- icant correlation between Bmi-1 expression and expres- sion of either p16Ink4a or p14ARF was evaluated in these ovarian carcinoma cohorts (P > 0.05, Fishers exact test). Discussion In recent years, the incidence of ovarian carcinoma has been increasing in Asian countries such as China and Singapore [24]. The available clinicopathologic prognos- tic indicators are not accurate, although the treatment of ovarian cancer has been improved greatly in recent years, its 5-year survival rate is of <30% [2]. Thus, it is important to identify a biological genetic molecular mar- ker that is associated with pathophysiologic processes of human ovarian cancer. The gene, Bmi-1, was initially shown to regulate hae- matopoiesis and differentiation of lymphocytes [25] and to be involved in cerebral development [26]. To date, the proto-oncogene Bmi-1 has been reported to be up- regulated in a large number of neoplasias, namely in lymphomas [27], cerebral tumours [26], breast cancer [13] and other epithelial tumours [28,29] and to be an oncogene associated with poor prognosis in various tumours [12]. To investigate whether or not the abnor- mal expression of Bmi-1 is involved in the pathogenesis of ovarian carcinoma, in the present study, the protein expression of Bmi-1 was examined firstly by IHC in nor- mal ovaries, benign and borderline epithelial ovarian tumors, and malignant epithelial cancers. The results demonstrated that the expression of Bmi-1 in all of the normal ovary specimens was absent or at low levels. In our ovarian tumor specimens, a significant increasing expression of Bmi-1 was observed from benign cystade- noma to borderline tumor, and to carcinoma. In addi- tion, we found that the frequency of intensive expression of Bmi-1 in undifferentiated ovarian carcino- mas was significantly larger than that in other types of carcinoma. In serous carcinomas, intensive expression of Bmi-1 was more likely to be observed in grade 2/3 Page 7 of 9 tumors than that in grade 1 tumors. Furthermore, inten- sive expression of Bmi-1 in our ovarian carcinoma cohorts was strongly correlated with an ascending histo- logical grade and clinical stage (pT/pN/pM and FIGO stage) of the tumor. These findings suggest that up- regulated expression of Bmi-1 in ovarian carcinoma may represent an acquired malignant phenotypic feature of tumor cells. Datas from several clinical studies show that abnormal expression of Bmi-1, in protein level as well as in gene level, is favorably associated with poor prognostic mar- kers and clinical outcome in diverse human cancers, such as colorectal cancer, nasopharyngeal carcinoma, bladder cancer and myelodysplastic syndrome [14,17-19]. However, to our best knowledge, there is lit- tle information about prognostic status and clinical out- come of Bmi-1 expression in ovarian cancer. This is the first study evaluating the expression of Bmi-1 by IHC, in association with clinicopathological and prognostic sig- nificance for a large number of ovarian cancer patients. Consistent with previous reports of other types of human cancer, in this study, we found that intensive expression of Bmi-1 in ovarian carcinoma was a predic- tor of short overall survival, independent of stage and grade. These findings raise the question of a potentially why important role of Bmi-1 as an underlying biological mechanism in the development and/or growth of human cancers. It is known, the encoded protein of Bmi-1, as well as other proteins from the PcG family, can block the tran- scription of some genes such as p16Ink4a and p19Arf involved in tumour suppression, resulting in oncogenic effects [14]. In our previous investigation, however, we found that Bmi-1 may promote immortalization of naso- pharyngeal carcinoma by modulating the expression of other genes, besides regulating p16Ink4a. Also, in the present study, we did not observe a significant correla- tion between Bmi-1 expression and either p16Ink4a or p14ARF expression in ovarian carcinoma cohorts. This data provided evidence that Bmi-1 does act through other molecular targets than repression of p16Ink4a/ p14ARF in ovarian carcinogenesis. Recently, it was reported that by applying a mouse/human comparative translational genomics approach, a Bmi-1-driven 11- gene signature was identified. This cohort of 11 genes was confirmed to be a magic marker of stem cell-ness and therapy failure in patients with a variety of aggres- sive tumors [18]. Clearly, further work needs to be done to more precisely understand the molecular mechanism of Bmi-1 in the development and progression of ovarian carcinoma, as well as other human cancers. With regard to the mechanism of up-regulated protein expression of Bmi-1 in ovarian carcinomas, it is known that gene amplification is a common pathological