Yang et al. BMC Cancer 2010, 10:133 http://www.biomedcentral.com/1471-2407/10/133 found to be significant on univariate analysis using the Cox regression model. For univariate survival analysis, we analyzed all ovarian carcinoma patients by Kaplan-Meier analysis. Log rank test was used to compare different sur- vival curves. P < 0.05 was considered significant. Results Bmi-1 expression in ovarian tissues Bmi-1 expression could be evaluated informatively in TMA tissues of 163/179 of ovarian carcinomas, 37/40 of borderline tumors and 26/30 of cystadenomas. The non- informative TMA samples included unrepresentative samples, samples with too few tumor cells (<300 cells per case) and lost samples. IHC staining of such non- informative samples were replaced and performed by using whole tissue slides. In our study, we defined that (-) and (+) were counted as low expression of Bmi-1, while (++) and (+++) were counted as intensive expres- sion of Bmi-1. According to this definition, the intensive expression of Bmi-1 was detected in 67/179 (37%) ovar- ian carcinomas. The increasing frequencies of Bmi-1 intensive expression in normal ovarian epithelium (0), to benign cystadenomas (3%), to borderline tumors (10%), and to invasive carcinomas were significant (37%, P < 0.05, Table 2). Association of Bmi-1 expression with ovarian carcinoma patient clinico-pathologic features The association between Bmi-1 expression in ovarian carcinomas and several known clinico-pathological fea- tures was further studied. Bmi-1 expression was posi- tively correlated with tumors histological type, grade, pT/pN/pM status, and FIGO stage (P < 0.05, Table 2). No significant correlation was obtained between Bmi-1 expression and patient age (≤ 50.7 years vs > 50.7 years) (P > 0.05, Table 1). Relationship between clinicopathologic variables, Bmi-1 expression and ovarian carcinoma patient survival: Univariate survival analysis In univariate survival analyses, cumulative survival curves were calculated according to the Kaplan-Meier Table 2 The expression of Bmi-1 in normal ovaries and in benign and malignant epithelial ovarian tumorsa Bmi-1 protein All cases Low expression Intensive expression Normal ovaries Cystadenomas Borderline tumors Invasive carcinomas 30 30 40 179 30 (100%) 29 (97%) 36 (90%) 112 (63%) 0 (0) 1 (3%) 4 (10%) 67 (37%) aValues are n (%). A significant increasing frequency of intensive expression of Bmi-1 was observed in cystadenomas, in borderline tumors and in invasive carcinomas (P < 0.01, Chi-Square Test for Trend) method. Differences in survival times were assessed with the log-rank test. First, to confirm the representativeness of the ovarian carcinomas in our study, we analyzed established prognostic predictors of patient survival. Kaplan-Meier analysis demonstrated a significant impact of well-known clinical pathological prognostic para- meters, such as tumor histological grade (p = 0.012), pT/pN/pM status (p < 0.01) and FIGO stage (p < 0.001) on patient survival (Table 3). The mean survival time for patients with tumors having intensive expression of Bmi-1 was 49.3 months compared to 100.3 months for pateints with tumors having low expression of Bmi-1 Table 3 Clinical pathological parameters and expression of Bmi-1 for prognosis of 179 patients with ovarian carcinoma by univariate survival analysis (log-rank test) All cases Mean survival (months) Median survival (months) Page 5 of 9 P value 0.388 0.491 0.012 0.003 <0.001 <0.001 <0.001 <0.001 Variable Age at surgery (years) ≤ 50.7a > 50.7 Histological type Serous(grade 1) Serous(grade2/3) Mucinous Endometrioid Clear cell Undifferentiated Histological grade (Silveberg) G1 G2 G3 pT1 pT2 pT3 pN0 pN1 pT status pN status pM status pMX pM1 FIGO stage I II III IV Bmi-1 expression Low Intensive aMean age bNot reached 92 87 11 107 23 8 7 23 36 101 42 51 35 93 88 91 153 26 33 21 99 26 112 67 83.4 81.7 110.4 63.4 75.8 116.7 102.8 32.7 104.9 85.9 48.0 109.5 82.2 66.5 100.9 52.8 94.8 21.5 134.2 115.0 71.5 21.5 100.3 49.3 136.0 55.0 136.0 52.0 NRb NR NR NR 136.0 64.0 29.0 NR NR 35.0 136.0 28.0 136.0 9.0 NR NR 37.0 9.0 136.0 22.0