Special Subtypes of Triple Negative Breast Carcinoma

Triple-negative breast cancer (TNBC) encompasses a diverse group of tumors lacking expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2. While conventional TNBC of no special type (IDC-NST) is often aggressive, histologically special subtypes such as metaplastic carcinoma, apocrine carcinoma, adenoid cystic carcinoma, IDC-NST medullary pattern and secretory carcinoma display distinct morphologic, immunophenotypic, and molecular hallmarks that markedly influence prognosis and therapy. Several of these entities have favorable outcomes or actionable targets (eg, androgen-receptor antagonists or TRK inhibitors). This article summarizes current knowledge on their classification, diagnostics, and clinical management, emphasizing opportunities for precision medicine in TNBC.