Molecular subtypes of invasive breast carcinoma of no special type, their correlation with histopathological features, Ki 67 index and tumor budding: A retrospective comparative study.

Context: Tumor budding (TB), poorly differentiated clusters (PDCs), and Ki 67 index are proven adverse prognostic factors in breast carcinoma. Though the relation of Ki 67 index with molecular subtypes of breast carcinoma have been extensively studied, there is very limited information on the role of TB and PDCs. Aims: To grade TB, PDCs, and Ki 67 index and assess histological features and relationship of all these with molecular subtypes of invasive breast carcinoma of no special type. Methods and Material: Retrospective study of 148 cases from 1/1/2019 to 30/12/2019. Division of molecular groups - Luminal A, Luminal B, Her2 neu positive, and triple-negative breast carcinomas (TNBC), and Ki 67 index grades based on St Gallen criteria, intratumoral and peritumoral TB and PDC grades as per the International Tumor Budding Consensus Conference (ITBCC) criteria for colon and correlation between these and other histological features with the molecular subtypes were done. Statistical Analysis: Chi-square test, univariate and multivariate logistic regression models were used. Results: Significant correlation was seen between TB and lymphovascular emboli, Luminal B tumors with high-grade TB and PDCs, Her 2 neu positive and TNBC tumors with low-grade TB, circumscribed tumor margins, tumor necrosis, and Luminal B, Her 2 neu positive and TNBC tumors with larger tumor size and high nuclear grades. Conclusions: TB and PDCs are useful in the prognostication of Luminal A and B tumors when the Ki 67 index values are low/intermediate. Her 2 neu positive and TNBC tumors have a high nuclear grade with necrosis and no association with TB or PDCs.