Histopathological subclassification of triple negative breast cancer using prognostic scoring system: Five variables as candidates

We attempted to subclassify triple negative breast cancer (TNBC) cases into subgroups according to clinical outcome or prognosis of TNBC patients using archival specimens. We analyzed 102 Japanese cases of invasive TNBC who underwent surgery between January 1998 and December 2007. The clinicopathological factors and clinical information were retrospectively retrieved from reviewing the charts of the patients. Immunohistochemical staining was performed for estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), epidermal growth factor receptor 1 (EGFR1), CK5/6, CK14, Ki-67, and CD31 for microvessel density (MVD). Median follow-up time of the patients was 68.5 months. Multivariable analysis demonstrated that pathologic node status was the most significantly associated with relapse-free survival (RFS) and breast cancer-specific survival (BCSS) of these patients. Pathological tumor size, basal-like type, Ki-67 labeling index (LI) and MVD were also independently associated with RFS and BCSS. Based on these results, we devised the risk score system reflecting hazard ratios of these prognostic factors above. With this system, TNBC patients in this study were classified into three subgroups (low-risk group: score 0-3, intermediate-risk group: score 4-7 and high-risk group: score 8-10). The significant difference of RFS and BCSS was detected among these three different subgroups of the patients (p<0.05). We propose the risk score system, which incorporated pathologic nodal status, size of the primary tumor, the presence or absence of basal-like features, Ki-67 LI, and MVD in order to predict postoperative clinical course of the Japanese TNBC patients.