Triple-Negative Breast Cancer: A Comprehensive Study of Clinical, Histomorphological, and Immunohistochemical...

Triple-negative breast cancers (TNBCs) are characterized by negative expression for estrogen (ER), progesterone (PR), and human epidermal growth factor 2 (HER2) receptors. Although the majority of basal-like breast cancers (BLBCs) diagnosed based on gene expression profiling belong to the TNBC group, both entities are not synonymous. Core BLBCs are TNBCs, which are positive for basal cytokeratin (CK) and/or epidermal growth factor receptor (EGFR). We aimed to study and correlate a TNBC cohort for various histomorphological features and immunohistochemical (IHC) profile in Indian patients. We studied 205 naïve TNBCs for histopathological features, which were further evaluated for basal CKs-namely, CK5/6, CK14, CK17-and EGFR expression to classify them as core BLBCs, using criteria of any basal CK and/or EGFR positivity and 7-negative phenotype (7NP). Among 205 TNBCs, 91% of cases were core BLBCs, and absence of ductal carcinoma in situ (DCIS) was significantly associated ( P = .014) with core BLBC. Geographic necrosis was correlated with expression of CK17 ( P = .002) and EGFR ( P = .038). A ribbon-like trabecular pattern and absence of DCIS were associated with CK17 ( P = .0002 and P = .043, respectively) and CK14 ( P = .04 and P = .0008, respectively). TNBC is a heterogeneous subgroup with adverse clinicopathological features, and many of them show significant correlation with basal CKs. TNBCs cannot be classified as core BLBC or 7NP based on morphological features, except absence of DCIS. However, this study illustrates the heterogeneity in TNBCs on the basis of IHC markers.