Understanding Triple-Negative Breast Cancer: Disease Overview and Defining Characteristics

Triple-negative breast cancer (TNBC) is an aggressive and heterogeneous subtype of breast cancer defined by the absence of estrogen receptor, progesterone receptor, and HER2 expression. Clinically, TNBC is more common in younger patients and is associated with higher rates of early recurrence and metastasis compared with other breast cancer subtypes. From a molecular standpoint, TNBC encompasses multiple biologic subgroups with distinct genomic and transcriptomic features, including frequent alterations in DNA damage–repair pathways and immune-related signatures. These molecular differences contribute to variable responses to therapy and have driven the development of targeted and immune-based treatment strategies. Clinically, TNBC often presents with high-grade tumors and rapid progression, underscoring the need for timely diagnosis and an individualized treatment approach. Together, its biologic complexity and aggressive clinical behavior make TNBC a challenging disease to manage.