Triple-Negative Breast Cancer: Intact Mismatch Repair and Partial Co-Expression of PD-L1 and LAG-3

Abstract

Background and aim: Poor response to immune checkpoint inhibitors (ICIs) has been observed in most triple-negative breast cancer (TNBC) cases (around 80%). Our aim was to investigate the status of mismatch repair (MMR), microsatellite instability (MSI), programmed death-ligand 1 (PD-L1), and lymphocyte-activation gene 3 (LAG-3) in TNBC.

Methods: A total of 74 TNBC samples were retrospectively analyzed. MMR and MSI were evaluated by immunohistochemistry (IHC) and polymerase chain reaction (PCR) using Promega 1.2 and NCI panels, respectively. PD-L1, LAG-3, and CD8 expression was assessed by IHC.

Results: None of the cases demonstrated deficient MMR (dMMR) or MSI. In total, 43/74 cases (58.1%) were PD-L1+, including 1 tumor PD-L1+, 25 tumor-infiltrating lymphocytes (TILs) PD-L1+, and 17 cases involving concurrence of tumor and TIL PD-L1+. The rate of TIL PD-L1+ was remarkably higher than that of tumor PD-L1+ (P<0.001). We identified 20 LAG-3+ cases (27.0%, 20/74), all of which were PD-L1+. Co-expression of PD-L1 and LAG-3 was noted in 46.5% (20/43) of the PD-L1+ population. In the LAG-3+ subtype (co-expression of PD-L1 and LAG-3), high correlation between TILs PD-L1+ and LAG-3+ was observed (P<0.01). A high frequency of CD8+ (98.6%, 73/74) was observed.

Conclusion: dMMR/MSI characteristics may not be a practical predictive marker for ICIs in TNBC. PD-L1+ is more common in TILs than in tumors. In the PD-L1+ population, approximately half of the cases showed LAG-3 co-expression. For patients with a poor response to PD-1(L1) mono ICI, dual blockade of PD-1(L1) and LAG-3 may be a viable option for the management of TNBC.

Keywords: CD8; LAG-3; PD-L1; microsatellite instability; triple-negative breast cancer.

Figure 1

MLH1, PMS2, MSH2, and MSH6 protein expression in 74 triple-negative breast cancer (TNBC) samples.

Figure 2

Representative images from pMMR/MSS triple-negative breast cancer (TNBC) in our cohort. The four MMR proteins (MLH1, PMS2, MSH2, and MSH6) (X200) all showed intact immunohistochemistry (IHC) staining. The microsatellite markers presented MSS both by Promega 1.2 and NCI panels. Promega 1.2 panel: BAT-25, BAT-26, NR-21, NR-24, and MONO-27; NCI panel: BAT25, BAT26, D2S123, D5S346, and D17S250.

Figure 3

Case no. 74 (A–C) showed tumor programmed death-ligand 1 (PD-L1)+, tumor-infiltrating lymphocytes (TILs) PD-L1+, lymphocyte-activation gene 3 (LAG-3)+, and CD8+ with 80%, 10%, 30%, and 70% positive cells, respectively (X200). (A) PD-L1 staining with clone E1L3N (A1. tumor PD-L1+/partial TILs PD-L1+; A2. TILs PD-L1+); (B) LAG-3 staining with clone D2G40; (C) CD8 staining with clone 4B11; Case no. 46 (D–F) showed tumor PD-L1+, TILs PD-L1-, LAG-3+, and CD8+ with 80%, 0%, 1%, and 90% positive cells respectively (X200). (D) PD-L1 staining with clone E1L3N (D1. tumor PD-L1+/TILs PD-L1-; D2. TILs PD-L1-); (E) LAG-3 staining with clone D2G40; (F) CD8 staining with clone 4B11; Case no. 34 (G–I) showed tumor PD-L1-, TILs PD-L1+, LAG-3+, and CD8+ with 0%, 10%, 10%, and 70% positive cells respectively (X200). (G) PD-L1 staining with clone E1L3N (G1. tumor PD-L1-; G2. TILs PD-L1+); (H) LAG-3 staining with clone D2G40; (I) CD8 staining with clone 4B11.

Figure 4

The status of programmed death-ligand 1 (PD-L1), lymphocyte-activation gene 3 (LAG-3), CD8 and Ki67 index in our series.