Written by: Debra Patt, MD, PhD, MBA
Content Sponsored by: Bristol Myers Squibb
Dr. Patt is a paid consultant for BMS and was compensated for her contribution in drafting this article.
Metastatic triple negative breast cancer (TNBC) is a devastating disease, making up 15% of all cancers, and having a limited outcome with an overall survival average of around a year.1,2 It is a diagnosis of exclusion, as tumor cells do not express the targetable hormone receptors (estrogen or progesterone receptors) or HER2, thus treatment options have historically relied on systemic chemotherapy rather than targeted treatment.3 This aggressive subtype is often associated with an earlier age of onset and an aggressive clinical course. Ethnic disparities have been identified for triple negative disease, with the incidence highest among patients who have a non-Hispanic black ethnic background compared to other ethnic groups.1 Furthermore, African American women are more likely to develop metastases compared to women of other races. Metastatic progression for triple-negative disease is generally characterized by early relapse and predominantly visceral (including liver, pulmonary and central nervous system) metastases.3
Historically, advances in the treatment of triple negative breast cancer have been rare. Multiple immunotherapy options in combination with chemotherapy are now approved in metastatic TNBC for patients with PD-L1 positive, first-line disease, and today there is much excitement about further evidence supporting its use in the metastatic and early stage settings.4 However, no head-to-head data exists to identify the optimal chemotherapy partner for checkpoint inhibition and not all chemotherapy agents appear to provide similar efficacy based on current data, hence more investigations are needed.5,6 Furthermore, while the incidence of immune-related adverse events such as endocrinopathies are low, the permanence of these side effects, particularly in the early stage setting, is concerning to some and should be closely monitored.
Germline BRCA mutations occur in approximately 10–30% of TNBC cases.7 In previously treated metastatic disease, the use of poly (ADP-ribose) polymerase (PARP) inhibitors in germline BRCA mutation positive patients has also shown improvements in survival, with the main reported side effects being hematologic, fatigue and diarrhea.3,8 In heavily pretreated metastatic TNBC patients, the use of antibody-drug conjugates has also resulted in anti-cancer effects.9
While advances in the aggressive and difficult-to-treat triple negative breast cancer subset are promising, all of these recent advances leave us with new treatment options but also unanswered questions. Our knowledge is limited and certainly will improve over time as we understand better predictors of outcome like PD-L1 expression, tumor infiltrating lymphocytes, and other factors as well as the importance of chemotherapy backbone choice. Other agents are now available for previously treated metastatic TNBC patients and further studies will be needed to assess the efficacy of these agents in earlier lines of therapy. Additionally, long-term follow up of studies will also be important to truly understand the impact of these new targeted approaches and the impact of drug tolerability on efficacy and patient quality of life.
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