Yang et al. BMC Cancer 2010, 10:133 http://www.biomedcentral.com/1471-2407/10/133 Page 6 of 9 Figure 2 Kaplan-Meier survival analysis according to Bmi-1 expression in 179 patients with invasive ovarian carcinoma (log-rank test). Probability of survival of patients: low expression of Bmi-1, n = 112; intensive expression of Bmi-1, n = 67 (p < 0.001). (P < 0.001, Fig. 2, Table 3). In stratified survival analysis, Bmi-1 expression could stratify the outcome of patients in hige-grade (grade 2/3) serous carcinoma (P = 0.045), mucinous carcinoma (P = 0.001) and undifferentiated carcinoma (P = 0.001) subgroups. Independent prognostic factors of ovarian carcinoma: Multivariate Cox regression analysis Since variables observed to have prognostic influence by univariate analysis may covariate, the expression of Bmi- 1 as well as other clinical pathological parameters that were significant in univariate analysis (pN stage and FIGO stage) was examined in multivariate analysis (Table 4). The expression of Bmi-1 was found to be an independent prognostic factor for poor overall survival (relative risk: 1.998, CI: 1.228-3.251, P = 0.005). Of the other parameters, pN stage (P = 0.010) and FIGO stage (P = 0.004) were also demonstrated as independent prognostic factor for overall survival. Amplification of Bmi-1 in ovarian tumor TMA In our FISH study, the FISH analysis was informative in 96/179 of ovarian carcinomas, 21/40 of borderline ovar- ian tumors and 15/30 of ovarian cystadenomas. Samples without FISH signal and samples with weak target signals Variable Bmi-1a Histological gradeb pT statusc pN statusd pM statuse FIGO stagef 1.998 0.940 1.189 2.016 0.975 3.686 Table 4 Multivariate analysis on overall survival (Cox regression model) Relative risk 95% Confidence interval P value 1.228-3.251 0.614-1.439 0.788-1.793 1.184-3.432 0.280-3.393 1.521-8.931 0.005 0.777 0.409 0.010 0.975 0.004 aIntensive expressin vs Low expression bG1 vs G2 vs G3 cpT1 vs pT2 vs pT3 dpN0 vs pN1 epMX vs pM1 fStage I vs Stage II vs Stage III vs StageIV or those with a strong signal background were the main reasons for most of the non-informative cases. FISH results demonstrated that the amplification of Bmi-1 was not detected in any of the ovarian cystadenoma and bor- derline tumor tissues; but was detected in 8% (8/96) of the informative ovarian carcinomas; in each of the 8 cases with Bmi-1 amplification, intensive expression of Bmi-1 was observed (Fig. 1E and 1F). In the remaining 88 informative cancers without amplification of Bmi-1,