Unveiling the Landscape of PD-L1 Expression and Tumor-Infiltrating Lymphocyte Subtypes in Advanced Triple-Negative Breast Cancer in Brazil

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Purpose: This study aimed to assess the frequency and prognostic significance of programmed cell death ligand 1 (PD-L1) expression and tumor-infiltrating lymphocyte (TIL) subtypes in advanced triple-negative breast cancer (TNBC). Patients and Methods: A database search was conducted to identify women with previously untreated locally recurrent inoperable or metastatic TNBC treated between January 2018 and December 2022. The inclusion criteria required formalin-fixed paraffin-embedded samples aged less than four years. PD-L1 expression was evaluated using the PD-L1 IHC 22C3 pharmDx assay, and the combined positive score (CPS) was calculated. TIL subtypes were assessed using immunohistochemical staining. Results: The study included 150 patients, with a median age of 51.5 years. The majority of patients were younger than 65 years, postmenopausal, non-white, and had metastatic TNBC. CPS≥10 was observed in 20.9% of cases, mainly in postmenopausal women. No significant differences were found in demographic characteristics and clinicopathological variables across PD-L1 subgroups. Tumors with PD-L1 CPS≥10 had higher expression of CD3+, CD4+, and CD8+ TIL subtypes. Most patients received first-line chemotherapy, with smaller proportions undergoing second, third, and fourth-line treatments. No statistically significant differences were observed in median progression-free survival (PFS) or overall survival (OS) across PD-L1 subgroups in this cohort of chemotherapy-treated patients. Conclusion: This study provides insights into the expression profiles of PD-L1 and TIL subtypes in advanced TNBC. The PD-L1 CPS status did not significantly affect survival outcomes, but variations in TIL subtype composition were observed based on PD-L1 CPS status.

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