Increased number of intratumoral IL-17+ cells, a harbinger of the adverse prognosis of triple-negative breast cancer

Introduction: Triple negative breast cancer (TNBC) is an aggressive cancer subtype and lack of effective targeted therapies. It has been recently reported that Interleukin 17 (IL-17), a family of cytokines secreted in tumor microenvironment, affects tumor progression through a variety of molecular pathways. Its role in TNBC is so far still poorly explored.

Materials and methods: We employed immunohistochemistry to evaluate the distribution of IL-17+ cells in TNBC with no special type features (TNBC-NST), their association with tumor microangiogenesis, as well as their impact on prognosis of the patients.

Results: In comparison to medullary carcinoma with triple-negative molecular features (TNBC-MC), we found a significant increase in IL-17+ cell infiltrates in intratumoral stroma and extratumoral stroma of TNBC-NST. Similarly, stromal cells with co-expression of CD4 and IL-17 were noted in intratumoral and extratumoral stroma in both TNBC-NST and TNBC-MC. In addition, intratumoral IL-17+ cells were positively associated with tumor cell expression of vascular endothelial growth factor A (VEGFA) and with intratumoral tumor microvascular density (MVD). Multivariate analysis identified that intratumoral IL-17+ cells (P = 0.018), MVD (P = 0.039), and TNM stage (P = 0.002) were independent prognostic factors for predicting poor PFS.

Conclusion: The study indicates that IL-17 is overexpressed in intratumoral stromal cells of TNBC-NST. The overexpression of IL-17 might engage in active tumor microangiogenesis through its signal transduction pathways resulting in increased tumor secretion of VEGFA, and then promote tumor progression. IL-17 might serve as a potential new target for individualized therapy to TNBC-NST patients by development of specific antibodies. Additional study is deemed to further explore the role of IL-17+ stromal cells in breast cancer.