24 - Triple-Negative and Basal-like Carcinoma

Abstract

Triple-negative breast cancer (TNBC) lacks expression of the estrogen receptor (ER), progesterone receptor (PgR), and human epidermal growth factor 2 (HER2) and accounts for approximately 15% of invasive breast cancers (IBCs). TNBC is a heterogeneous category of carcinoma subtypes. The vast majority are high-grade IBCs of no special type (IBC-NST, aka invasive ductal carcinoma [IDC]) with a basal-like intrinsic subtype and aggressive clinical behavior. However, some basal-like TNBCs are lower-grade carcinomas with more favorable outcomes, including adenoid cystic carcinoma, secretory carcinoma, low-grade adenosquamous carcinoma, and fibromatosis-like metaplastic carcinoma. Refined classification of breast cancer subtypes yields important biological and clinical information. A greater understanding of the molecular underpinnings of TNBC and of the tumor immune microenvironment have led to the first targeted therapies for patients with TNBC. This chapter covers the molecular, clinical, morphological, and prognostic features of the basal-like, triple-negative IBC-NST, with an emphasis on novel and emerging biomarkers and treatments.