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

Background and 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 Cytokeratin 5/6 (CK 5/6), Epidermal Growth Factor Receptor 1 (EGFR 1), Ecadherin 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 Chisquare 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.