Subclassifying triple-negative breast cancers and its potential clinical utility.

The molecular subtyping of triple-negative breast cancer (TNBC) is critical to guiding individualized patient treatment. In this study, we sought to characterize the clinicopathologic features of TNBC subtypes and to identify correlates of patient survival in an effort to provide a robust foundation for treatment planning. We additionally assessed PD-L1 expression in Chinese TNBC patients and evaluated the relationship between such expression and immunotherapeutic treatment outcomes. Based on analyses of histologic characteristics including apocrine differentiation, tumor-infiltrating lymphocytes, and metaplastic features, we selected immunohistochemical (IHC) markers including CD8, FOXC1, and AR for use in classifying TNBC cases. Associations between these subtypes and a range of clinicopathologic characteristics were evaluated. We classified a cohort of 93 TNBC patients into individuals with luminal androgen receptor (LAR), immunomodulatory (IM), basal-like immune-suppressed (BLIS), and mesenchymal (MES) tumor subtypes (23, 24, 39, and 7 cases, respectively). PD-L1 positivity was observed in 49.6% of cases and was more common in individuals with IM subtype disease. Mismatch repair deficiency (dMMR) was observed in just one patient. Significant differences in histologic grade, pT stage, lymphocyte distribution patterns, large scarring areas without cells in tumor of central (central scar), and PD-L1, P53, and Rb status were observed among these TNBC subtypes, whereas no such differences were observed with respect to age, invasion pattern, or pN stage. Rates of disease progression were higher at the 40-50 month follow-up time point, but there were no significant differences in recurrence-free survival or breast cancer-specific survival among these subtypes. IHC markers associated with clinicopathologic characteristics represent a powerful approach to TNBC molecular typing, providing a foundation for precision patient treatment. PD-L1 expression may represent a relevant factor in TNBC patient immunotherapeutic treatment planning, whereas dMMR is not likely to be of substantial value when evaluating immunotherapeutic efficacy in these patients.