Immunohistochemical Characterization of Breast Carcinoma: Clinical Correlations, Molecular Subtypes, and Therapeutic Implications

Abstract

Background: Breast carcinoma exhibits heterogeneity in terms of morphology, molecular, treatment response, and clinical outcomes. The objective of the study was to classify the various malignant breast cancer cases based on their immunohistochemical characteristics and understand their association and behavior, which may be useful for predicting treatment and prognosis. Methods: In this study, 12808 malignant breast cancer cases were studied based on hormone receptor IHC biomarkers, age, gender, histological type, grade and molecular classifiers. Results: The mean age of patients was 53.63+13.08 years, around 45.43% were grade 3 tumors and the invasive duct carcinoma of non-specified type (NST) was the most common type seen (93.83%). ER positivity was 83.89% in grade 1, 69.9% in grade 2, and 36.86% in grade 3 tumors, and the overall PR and Her-2 positivity was 47.06% and 18.67%, respectively. A relatively higher percentage of Triple Negative cases was seen (36.58%), followed by 25.43% Luminal A cases. There was a significant association between molecular subtypes with respect to age, gender, Scarff Bloom Richardson (SBR) grade, and histological type (P<0.0001). Overall, grade 3 tumor cases were most common, the majority of which were Triple Negative. Maximum cases of triple negative tumors were seen among women, being mostly concentrated in younger age group i.e. <40 years. Conclusion: Immunohistochemistry for hormone receptor positivity remains the mainstay of diagnosis and molecular sub-classification. The hormone response of tumors is important prognostically, in predicting the treatment outcomes. Going further, molecular analysis and gene expression studies can further augment the histopathological diagnosis to assist strategies of targeted therapy and precision medicine resulting in better patient outcomes.