Comparative Analysis of Stromal Tumor Infiltrating Lymphocytes in Various Grades and Molecular Subtypes of Breast Carcinoma

BACKGROUND: Stromal tumor-infiltrating lymphocytes (sTILs) reflect host immune response and have growing relevance in breast cancer prognostication. Their distribution varies across tumor grades and molecular subtypes, yet data from the Indian population remain limited. This study evaluated sTIL patterns in invasive breast carcinoma and their association with clinicopathological features. MATERIALS AND METHODS: A prospective observational study of 152 histologically confirmed breast carcinoma cases was conducted at a tertiary center in North India. sTILs were assessed on hematoxylin and eosin sections following the International TILs Working Group 2014 guidelines. Tumors were classified by histological grade and molecular subtype triple-negative breast cancer (TNBC vs. non-TNBC). Associations between sTIL categories and key clinicopathological variables were analyzed using Chi-square, Kruskal-Wallis, and correlation analyses. RESULTS: Low sTILs were most common (80.3%), followed by intermediate (14.5%) and high (5.3%). High sTILs showed a strong association with higher grade; 62.5% of high-sTIL tumors were grade III (P < 0.001). Larger tumors (>5 cm) demonstrated higher sTILs (P < 0.001). ER-negative and PR-negative tumors showed progressively higher sTIL levels (P < 0.001). TNBC exhibited the greatest immune infiltration, comprising 87.5% of high-sTIL tumors (P < 0.001). sTILs showed positive correlations with grade, tumor size, TNBC status, and Ki-67 proliferative index, and negative correlations with estrogen receptor and progesterone receptor expression. No significant associations were found with lymph node or human epidermal growth factor receptor 2 status. CONCLUSION: sTILs vary markedly across breast cancer subtypes and correlate with aggressive pathological features, particularly TNBC, high-grade, hormone receptor negativity, and high proliferative index. Incorporating standardized sTIL assessment into routine reporting may help identify tumors with active immune microenvironments.