Breast Cancer Res Treat (2008) 107:249–257 253 Fig. 1 TMA core showing stromal mast cells stained with c-kit (CD- 117). Magniﬁcation, 20·. MCs are seen as brown, granular stained oval, spindle or polygonal cells was a favourable prognostic marker in the entire training set (BCSS @ 18.4 years, Log rank [Mantel Cox], P = 0.001). Correlation with other biomarkers There was positive correlation between MCs and ER (Kendall’s tau-b [sb], 0.034, P = 0.148), Bcl2 (sb = 0.077, P = 0.002), and Her2 (sb = 0.049, P = 0.052), and nega- tive correlation between MCs and EGFR (sb = –0.029, P = 0.228) and CK5/6 (sb = –0.003, P = 0.906) in the training set analysis (Table 3). As these correlations were either not signiﬁcant or extremely weak, they were not carried forward to the validation set for further analysis. Nodal status KM survival analysis showed no statistically signiﬁcant difference in the survival between tumors with and without MCs in node-negative (BCSS @ 18.1 years, Log rank [Mantel Cox], P = 0.1199) and a signiﬁcant difference in the node-positive group (BCSS @ 18.3 years, Log rank [Mantel Cox], P = 0.0140). Hence, this result was also not carried forward to the validation set. Multivariate analysis Cox proportional hazard model was used to carry out the multivariate analysis and included age, tumor grade, tumor size, nodal status, ER and Her2 as independent predictors of BCSS. All the above variables achieved statistical signiﬁcance as shown in Table 4(a). Presence of MCs Fig. 2 KM survival curve for all patients in training set (a) and validation set (b) with presence of stromal mast cells achieved statistical signiﬁcance (P = 0.041) with a HR = 0.804, 95% CI 0.653–0.991. Validation set results Survival analysis This group included the remaining 2,222 patients from the whole cohort. The mean age at diagnosis was 60 years and the median follow-up was 12.4 years. The median tumor size was 2.0 cm. 50% of patients had Grade 3 tumors, 43% were node positive, and 76% were ER positive. After excluding cases that had insufﬁcient invasive tumor, missing core or un-interpretable staining pattern, 1,796 cases were carried forward for the analysis. Out of these, MCs were present in 494 (27.5%) cases. KM survival analysis (Fig. 2b) showed that the presence of stromal MCs 123