A Novel Subset of Triple-Negative Breast Cancers with Unique Histology and Immunohistochemical Expression.

Background & Objective: Triple-Negative Breast Carcinoma (TNBC) is characterized by an absence of estrogen receptor, progesterone receptor and HER2 neu expression, with distinct molecular, histological and clinical features, aggressive clinical course and a poor prognosis. The objective was to evaluate the expression of Cytokeratin5/6 (CK 5/6), Epidermal Growth Factor Receptor 1 (EGFR 1), E-cadherin and Androgen receptor in tissue sections of TNBC. Methods: All modified radical mastectomy samples received negative for the three markers were subjected to further studies with CK5/6, EGFR 1, E- cadherin and Androgen receptor staining. The clinical and pathological data were tabulated and statistically analysed using the Chi-square test, and cross-tabulation was done to assess the correlation between these markers. Results: Of 94 samples classified as TNBC, 31 (33%) were positive for CK 5/6, 47 (50%) for EGFR, 32 (34%) for E Cadherin and Androgen receptor, respectively. We had one positive patient for all four markers, 13 patients were negative for all four. Thirty-five cases were positive for only one marker, 32 were positive for two markers, and 13 were positive for three markers. Analysis revealed certain interesting patterns, namely - E cadherin was the most common isolated marker expressed in our cohort of TNBC with 15 of 35 positives. Conclusion: This study highlights the presence of a unique subtype of TNBC, which are negative for all the four markers studied here, with unique histomorphology of absent tumour necrosis and stromal lymphocytic infiltration being unique.