Chemotherapy is the primary established systemic treatment for patients with triple-negative breast cancer (TNBC) in both the early and advanced-stages of the disease. The lack of targeted therapies and the poor prognosis of patients with TNBC have fostered a major effort to discover actionable molecular targets to treat patients with these tumours. Massively parallel sequencing and other 'omics' technologies have revealed an unexpected level of heterogeneity of TNBCs and have led to the identification of potentially actionable molecular features in some TNBCs, such as germline BRCA1/2 mutations or 'BRCAness', the presence of the androgen receptor, and several rare genomic alterations. Whether these alterations are molecular 'drivers', however, has not been clearly established. A subgroup of TNBCs shows a high degree of tumour-infiltrating lymphocytes that also correlates with a lower risk of disease relapse and a higher likelihood of benefit from chemotherapy. Proof-of-principle studies with immune-checkpoint inhibitors in advanced-stage TNBC have yielded promising results, indicating the potential benefit of immunotherapy for patients with TNBC. In this Review, we discuss the most relevant molecular findings in TNBC from the past decade and the most promising therapeutic opportunities derived from these data.

Triple-negative breast cancer: challenges and opportunities of a heterogeneous disease

Triple-negative breast cancer, characterized by tumors that do not express estrogen receptor (ER), progesterone receptor (PR), or HER-2 genes, represents an important clinical challenge because these cancers do not respond to endocrine therapy or other available targeted agents. The metastatic potential in triple-negative breast cancer is similar to that of other breast cancer subtypes, but these tumors are associated with a shorter median time to relapse and death. One important goal is therefore the identification of prognostic factors and markers to reliably select high and low risk subsets of patients with triple-negative disease for different treatment approaches of subtypes with differential responsiveness to specific agents. However, a reliable prognostic marker has been elusive, and markers have been inconsistently useful. For example, epidermal growth factor receptor (EGFR) has been studied, but there is still a lack of agreement on a standard assay or cutoff for EGFR expression levels with respect to prognosis. Similarly, because triple-negative status is sometimes used as a surrogate for basal-like breast cancer, specific basal markers have been explored. Indeed, trials designed to accrue patients with basal-like breast cancer using ER/PR and HER-2 negativity may provide only an approximation of the triple-negative population and are sometimes reanalyzed using more specific indicators like CK 5/6, EGFR status, and others, again marred by discordances. Chemotherapy remains the mainstay of treatment of triple-negative breast cancer, but important limitations still need to be overcome in the next few years if any significant clinical strides are to be made. Current treatment strategies for triple-negative disease include anthracyclines, taxanes, ixabepilone, platinum agents, and biologic agents. More recently, EGFR inhibition has been proposed as a therapeutic mechanism in triple-negative breast cancer, again with mixed results. Agents that target poly(ADP-ribose) polymerase and androgen receptors have also been proposed in these patients or subsets of them, and ongoing trials should result in definitive guidance with respect to the value of these agents in triple-negative disease. Triple-negative breast cancer is clearly a distinct clinical subtype, from the perspective of both ER and HER-2 expression, but further subclassification is needed. At present, there is not a clear, proven effective single agent that targets a defining vulnerability in triple-negative breast cancer. This article will review the clinical problem of triple-negative disease, potential prognostic factors, demonstrated efficacy of currently available therapeutic options, and new potential therapies.

Triple-Negative Breast Cancer: An Unmet Medical Need

Triple-negative breast cancer—current status and future directions

Purpose
Triple-negative breast cancer (TNBC) is a heterogeneous group of tumors comprising various breast cancers simply defined by the absence of estrogen receptor, progesterone receptor and overexpression of human epidermal growth factor receptor 2 gene In this review, we discuss the epidemiology, risk factors, clinical characteristics and prognostic variables of TNBC, and present the summary of recommended treatment strategies and all other available treatment options

An Overview of Triple-Negative Breast Cancer

Cytotoxic chemotherapy remains the mainstay of treatment for triple-negative breast cancer (TNBC) despite the promise of new targeted and biologic agents. Many studies have shown significant benefit of chemotherapy in the neoadjuvant, adjuvant, and metastatic treatment of TNBC. Neoadjuvant chemotherapy studies have consistently reported higher response rates in TNBC than non-TNBC, and pathologic complete response has been shown to predict improved long-term outcomes for TNBC. Although the specific adjuvant regimens that may be most effective for TNBC are still being determined, third-generation chemotherapy regimens using dose dense or metronomic polychemotherapy are among the most effective tools presently available. The role of specific chemotherapy agents in the treatment of TNBC remains incompletely defined and warrants careful review to ensure that the most effective therapy is delivered while minimizing unnecessary toxicity. Platinum agents have seen renewed interest in TNBC based on a growing body of preclinical and clinical data suggesting encouraging activity. Taxanes and anthracyclines are active in TNBC and remain important agents but have not shown specific benefit over non-TNBC. Capecitabine has limited reported data in TNBC, but some reports suggest differential activity in TNBC compared with hormone receptor-positive breast cancer. TNBC is itself a heterogeneous group in which subgroups such as BRCA1 mutation carriers may have particular sensitivity to platinum agents and relatively less sensitivity to taxanes. Therefore, the identification of additional molecular biomarkers to predict response to specific chemotherapy is required to further improve treatment strategies with the current menu of chemotherapy options and future combinations with targeted therapies.

Triple-negative breast cancer: role of specific chemotherapy agents.

Triple-negative high-risk breast cancer derives particular benefit from dose intensification of adjuvant chemotherapy: results of WSG AM-01 trial

The proto-oncogene c-kit is known to be expressed in poorly differentiated breast cancer. In this study, we retrospectively evaluated the prognostic and predictive impact of c-kit in a high risk subgroup of breast cancer patients (>9 axillary node metastases) who received high-dose (HDCT) or dose-dense (DDCT) conventional chemotherapy and correlated these findings with the expression of the basal-type markers CK5 and CK 17, estrogen (ER) and progesterone (PR) receptor, Her-2/neu and MIB 1. C-kit, CK5, CK17, ER, PR, Her-2/neu and MIBI expression was evaluated immunohistochemically using tissue microarrays containing breast cancer samples from 236 patients who were randomized to the WSG AM01 trial (median follow-up of 60 months). There was a significant overall survival (OS) benefit for patients receiving HDCT compared to DDCT (p = 0.027). C-KIT expression was found in 12 % of all breast cancers and correlated with a poorer OS in multivariate analysis (p = 0.051). Furthermore, c-kit correlated with high grade (p = 0.019), CK5- and CK17-positivity (p <0.0001 and p = 0.001, respectively) and ER- and PR-negativity (p = 0.04 and p = 0.008, respectively). In contrast to CK5 and CK17, patients with c-kit positive breast cancers revealed no benefit from high-dose chemotherapy. These findings underline that c-kit expression represents an independent negative prognostic marker in high-risk breast cancer. Correlation with CK5 +/CK17+ and ER-/PR-suggests that c-kit positive carcinomas are at least partly of basal-type.

G. Schütt

Papers

Triple-negative high-risk breast cancer derives particular benefit from dose intensification of adjuvant chemotherapy: results of WSG AM-01 trial

C-kit expression in high-risk breast cancer subgroup treated with high-dose or conventional dose-dense chemotherapy.