Immunophenotypic and Morphological Profile of Basal like and non Basal like Invasive Breast Carcinoma

Introduction: Breast carcinomas are heterogeneous disease with different prognosis and therapy responses despite similarities in histological types, grade and stage. Recently, gene expression profiling, a method using cDNA microarray to explore gene expression patterns, has classified breast cancer into 5 distinct subtypes based on variations in gene expression patterns. These 5 subtypes are luminal A and luminal B, normal breast like, Human Epidermal Growth Factor Receptor 2 (HER2) over expressing, and basal-like subtypes. A panel with four antibodies including ER, c-ERB-B2, EGFR and CK5/6 can be used to define Basal-like Breast Carcinoma (BLBC) with 55-76% sensitivity and 100% specificity. BLBCs have been defined as ER-ve, PR-ve, and c-ERB2-ve, CK5/6 and / or EGFR +ve tumours. Aim: To evaluate the expression of cytokeratin 5/6, EGFR, vimentin, ER, PR and Her2/neu in all invasive breast carcinomas. To classify invasive breast carcinomas into basal like and non basal like breast carcinomas according to immunophenotypic pattern and to correlate the immunophenotypic profile of basal like and non basal like with morphological pattern. Materials And Methods: Total 80 cases of invasive breast carcinoma were categorised into basal like and non basal like breast cancer by immunohistochemistry. BLBC was defined as a triple negative tumour with cytokeratin 5/6 and/or EGFR positivity. Morphological patterns of two groups were compared. Statistical analysis was performed using Student’s ‘t’-test for the comparison of mean value by SPSS 20 software. Results: The prevalence of BLBC was 26.3%. Patients with BLBC were younger (p=0.009) and had higher tumour grades (p=0.001). Morphologic features of BLBC include increased mitosis, nuclear pleomorphism, high tubular grade and stromal lymphocytic response. Univariate analysis showed significant association of BLBC with mitosis, tubular grade, nuclear grade, stromal lymphocytic response and histological grade (p=0.001). On multivariate analysis, BLBC were associated with high mitotic number (p=0.003), high tubular grade (p=0.01) and nuclear grade (p=0.01). Vimentin was positive in 76.2% of BLBCs, while cytokeratin was less frequently expressed (38.1%). Conclusion: BLBCs have distinctive morphological features however not pathognomic. Knowing these features and addition of immunohistochemical markers can help to reach the definitive diagnosis of BLBCs