The pathological and clinical landscape of refractory metastatic triple negative breast cancer: a narrative review

Triple negative breast cancer (TNBC) refers to a special subtype of breast cancer that is negative for the estrogen receptor, the progesterone receptors, and human epidermal growth factor receptor 2. As a group of diseases, it has strong heterogeneity. Refractory metastatic triple negative breast cancer (mTNBC) has even greater heterogeneity, more susceptibility to drug resistance, and faster progression, which makes it more difficult to treat effectively and significantly reduces a patient's overall survival. Therefore, in order to overcome this difficulty in clinical practice, we need to deeply understand the special subgroup by analyzing definition and prognostic factors of refractory mTNBC and describing the therapeutic status and future treatment directions.Recent domestic and foreign guidelines, as well as clinical studies related to refractory mTNBC on PubMed and the China National Knowledge Infrastructure (CNKI) databases were retrospectively analyzed. The six keywords we selected were used for literature search. Two authors performed database searches independently, and disagreements over the results were mediated by a third reviewer.According to the guidelines, refractory mTNBC has not been clearly defined. Related studies indicated that tumor heterogeneity may be one of the main mechanisms of early relapse or drug resistance in refractory mTNBC. The clinical treatment options for refractory mTNBC are very limited. Although chemotherapy is the standard treatment, it is limited by poor efficacy and intolerance in the clinical stage. Therefore, in recent years, many studies have explored novel treatment options. Both immunotherapy and poly(ADP-ribose) polymerase (PARP) inhibitors have been selected as first-line treatment in clinical studies, but gained limited benefits. Indeed, clinical studies have shown good efficacy with novel ADCs, which may be promising in the clinical treatment of refractory mTNBC.Currently, improving the survival time and quality of life of refractory mTNBC are major challenges for clinicians. Novel therapies including immunosuppressive agents, PARP inhibitors, and ADCs rather than chemotherapy alone have achieved good results in the exploration of first-line treatment for refractory TNBC patients, but this warrants further research and investigation.