Stromal Tumor Infiltrating Lymphocytes (sTIL) as an Independent Predictor of Pathologic Response to Neadjuvant Chemotherapy in Breast Cancer in Indonesia: A Hospital-based Study

Objective: We aim to describe the sTIL profiles of Indonesian breast cancer patient and its role in predicting neoadjuvant chemotherapy response. Method: This retrospective cohort study used secondary data from the archive of Anatomic Pathology Department FMUI/CMH. We did total sampling of 62 cases of locally advanced breast cancer cases that were biopsied, had neoadjuvant chemotherapy, and operated on from 2015 to 2020. We collected the clinicopathological data of each sample, measured the sTIL intensity in the biopsy specimen and evaluated the chemotherapy response from the mastectomy specimen using residual cancer burden (RCB) scoring method. Multivariate linear regression determined the independent predictors of RCB score. Result: There were 62 female patients, 45.2% were Luminal-HER2-, 43.5% were HER2+, and 11.3% were triple negative (TN). Most sTIL intensity (59.7%) were low (median 10%; 1%-60%). Moderate-high sTIL intensity was associated with HER2+ type, while low sTIL was with luminal-HER2- (p=0.038). Only 8.1% patients achieved pCR. Statistically different median sTIL intensity in minimal, moderate, and extensive burden group were 28%, 20%, and 8%, respectively (p=0.002). sTIL was an independent predictor for better response (lower RCB score), which were 0.07 (95% CI 0.04-0.09) lower for every 1% increase in sTIL intensity.Conclusion: sTIL intensity was mostly low in Indonesian breast cancer patient. However, it can predict neoadjuvant chemotherapy response, with 0.07 lower RCB score for every 1% increase of sTIL intensity.