Albergaria et al. BMC Cancer 2011, 11:299 http://www.biomedcentral.com/1471-2407/11/299 Page 6 of 10 Table 2 Nottingham Prognostic Index components on triple-negative and non-triple-negative breast cancer subtypes Molecular Subtype Luminal HER-OE Triple Negative (TNBC) Statistics TNBC vs Tumour Size Mean ± St. Error 2.92 cm ± 0.105 (N = 302) 3.08 cm ± 0.203 (N = 93) 3.70 cm ± 0.211 (N = 155) Luminal HER2-OE P-value* p < 0.001 P = 0.05 Nottingham Prognostic Index Components Tumour Grade I 24.1% 4.9% 4.9% II 38% (N = 324) 16.5% (N = 103) 23.9% (N = 163) P-value** < 0.0001 III 38% 78.6% 71.2% None 43.9% 42.4% 48.6% Lymph Node Status 1 < LNS < 3 26.7% (N = 262) 24.2% (N = 99) 25% (N = 148) P-value** Not significant LNS > 3 29.4% 33.3% 26.4% *ANOVA was used to compare the means of the three groups ** P-values were calculated with the use of the c2 test lymph nodes presented a NPI > 5.4 (Additional file 1), showing that LNS is a determinant factor to predict worse prognosis in TNBC patients. Tumour size is theoretically associated with the increased likelihood of lymph node invasion in breast cancer. In fact, we demonstrated that in non-TNBC there was a strong association (p < 0.0001) between tumour size and LNS, where 47% of patients with tumours larger than 5 cm presented extensive metastiza- tion (Table 3). In TNBC patients, 44% of patients with larger tumours also showed a significant trend (p < 0.001) to display more extensive lymph node invasion (Table 3). An additional analysis was also performed considering the presence or absence of lymph nodes involved, and herein, we observed that 61% of TNBCs with sizes < 2 cm lacked lymph node involvement, whereas approximately 78% of TNBCs with sizes > 5 cm displayed axillary lymph node invasion. These results showed that larger tumours frequently metastasize to lymph nodes, either being non-triple negative or TNBC lesions. Significance of NPI components to breast cancer survival and mortality risk in TNBC patients To evaluate the relevance of each NPI component to the survival of TNBC patients we used the follow-up data available for the TNBC cohort and survival curves were estimated by the Kaplan-Meier method. Survival curves demonstrated that TNBC patients with larger breast tumours showed a significant difference towards worse survival time (p < 0.0001; Figure 2A). Similarly, TNBC patient survival is seriously affected by the lymph node status (p < 0.0001; Figure 2B). As previously demonstrated by univariate hazard ana- lysis [50], we also showed that tumour size, histological grade and lymph node status were significant predictors of overall survival in breast cancer series. The same Cox proportional analysis was used to estimate the risk asso- ciated to the survival difference found by Kaplan-Meier curves in TNBC cohort. We observed that tumour size was a significant predictor of survival in this subset of tumours, showing that patients with larger tumours carry about 3.2-fold-increased risk of breast cancer- Table 3 Association of tumour size and lymph node status in triple-negative and non-triple-negative breast cancer Non-Triple Negative Breast Cancer Triple Negative Breast Cancer LNS None 1 < LNS < 3 LNS > 3 None 1 < LNS < 3 LNS > 3 TS Tumour Size < 2 cm Tumour Size 2-5 cm Tumour Size > 5 cm Statistics 66.7% 39.4% 19.4% (N = 276) 22.7% 26.1% 33.3% P-value* < 0.0001 10.7% 34.5% 47.2% 60.8% 56.7% 22.2% (N = 145) 32.1% 19.8% 33.3% P-value* < 0.001 7.1% 23.5% 44.5%