PD-L1 protein expression in breast cancer.

Area of Science:

• Oncology
• Immunology
• Pathology

Background:

• Programmed cell death-ligand 1 (PD-L1) is an immune checkpoint marker expressed on cancer cells and tumor-infiltrating immune cells (TICs).
• PD-L1 is a potential immunotherapy target, particularly relevant in triple-negative breast cancer.
• Understanding PD-L1 expression patterns is crucial for predicting treatment response and patient outcomes.

Purpose of the Study:

• To evaluate the prognostic significance of PD-L1 expression in both tumor epithelial cells and TICs in breast cancer patients.
• To investigate associations between PD-L1 expression and histopathological characteristics, proliferation, and molecular subtypes.
• To determine the differential expression of PD-L1 in various breast cancer subtypes.

Main Methods:

• Immunohistochemistry was used to assess PD-L1 expression in tissue microarrays from 821 breast tumors.
• PD-L1 expression was quantified separately in epithelial and stromal compartments.
• Statistical analyses, including Pearson's chi-squared test and Cox regression, were employed to correlate PD-L1 levels with tumor characteristics and patient prognosis.

Main Results:

• PD-L1 expression (≥1%) was observed in 6.5% of tumor epithelial cells and 17.6% of TICs.
• PD-L1 expression in TICs was significantly associated with high histopathological grade, increased proliferation, and medullary/metaplastic patterns.
• Higher PD-L1 expression in TICs was noted in HER2-positive and basal-like breast cancer subtypes.

Conclusions:

• PD-L1 expression is more prevalent in TICs compared to tumor epithelial cells in breast cancer.
• TIC PD-L1 expression is linked to aggressive tumor features and non-luminal subtypes.
• PD-L1 expression in either compartment did not demonstrate an independent association with patient prognosis.