Clinicopathologic features and prognoses of different histologic types of triple-negative breast cancer: A large population-based analysis.

PURPOSE: To examine the clinicopathologic characteristics and survival outcomes of different histologic types of triple-negative breast cancer (TNBC).

METHODS: We used the SEER database to identify patients with TNBC diagnosed between 2010 and 2014. Our analysis focused on the seven most prevalent histologic types. Differences were compared between invasive carcinoma of no special type (NST) and the other six types.

RESULTS: Significant differences were observed in age at diagnosis, tumor grade, size, nodal status and treatment. As tumor size increased, the number of positive lymph nodes increased markedly in invasive lobular carcinoma (ILC) and mixed NST and lobular carcinoma (NST-ILC), while in metaplastic carcinoma the number only increased slightly. In multivariate survival analyses, compared with patients with invasive carcinoma NST, breast cancer-specific survival (BCSS) and overall survival (OS) were worse for those with NST-ILC (BCSS: hazard ratio [HR] 1.81, P < .001; OS: HR 1.56, P = .005) or metaplastic carcinoma (BCSS: HR 1.95, P < .001; OS: HR 1.73, P < .001). By contrast, patients with medullary (HR 0.40, P = .010) or apocrine carcinoma (HR 0.27, P = .008) showed better BCSS. Time-dependent receiver operating characteristic (ROC) analyses indicated that T category in ILC and N category in metaplastic carcinoma were of less prognostic value.

CONCLUSIONS: According to the histologic classification of TNBC, this heterogeneous disease can be divided into several entities with different clinicopathologic features and prognoses. In the era of molecular subtyping of breast cancer, the histologic classification of TNBC is still of considerable clinical significance.