P14.03 Increased Tumor-Associated LAG-3+ Lymphocytes Correlate with Aggressive Tumor Behavior and Worse Prognosis in Lung Adenocarcinoma

Abstract

Immune checkpoint blockade targeting the PD-1/PD-L1 axis has become a mainstay of treatment for advanced non-small cell lung cancer. However, only a subset of patients benefits, with long-term efficacy limited by primary and secondary resistance. Resistance to PD-1 axis blockade is attributed in part to the upregulation by T-lymphocytes of regulatory molecules such as lymphocyte activation gene-3 (LAG-3). This study examined the role of LAG-3+ T-lymphocytes in the lung adenocarcinoma microenvironment through correlation with clinicopathologic features and patient outcomes. Immunohistochemistry for LAG-3 and CD8 was performed on 225 lung adenocarcinomas resected in 2010-2012 using tissue microarrays (duplicate of 2-mm core). The number of LAG-3+ lymphocytes was quantified in 3 high-power fields (HPF; each 0.24 mm2) for each of the two duplicate samples, and CD8+ tumor-associated lymphocytes (both stromal and tumor-infiltrating) were also quantified. LAG-3+ lymphocytes, CD8+ T-cells, and the ratio of LAG-3+/CD8+ T-cells were correlated with clinicopathologic features, PD-L1 expression, and patient outcomes. In lung adenocarcinomas from 225 patients (141 women, 84 men; age 39-89 [median 69] years; 79% smokers; 88% stages 1-2; 40.4% KRAS-mutant; 21.3% EGFR-mutant), the number of LAG-3+ cells ranged from 0 to 540.1/mm2 (median 7.0/mm2), and the number of CD8+ tumor-associated lymphocytes ranged from 34.8 to 5205.3/mm2 (median 626.7/mm2). Higher numbers of LAG-3+ cells were associated with smoking history (p<0.001) and features of aggressive tumor behavior, including solid-predominant histologic pattern, presence of lymphovascular invasion, and presence of nodal metastasis (all p<0.01). Larger overall tumor size and invasive tumor size correlated with LAG-3+ cells when normalized to CD8+ cell counts (LAG-3/CD8 ratio; p<0.05). In terms of molecular features, KRAS-mutant tumors were associated with significantly higher numbers of LAG-3+ cells versus EGFR-mutant tumors (p<0.01). LAG-3+ cell count was positively correlated with both PD-L1 H score and CD8+ tumor-associated lymphocytes (all p<0.01). Lastly, patients with tumors harboring an increased LAG-3/CD8 ratio (i.e., above the median) showed significantly worse overall survival, irrespective of PD-L1 expression (p=0.027). Increased LAG3+ T-lymphocytes were associated with smoking history, adverse histologic features, worse survival, and increased PD-L1 expression in lung adenocarcinomas. Given the known role of LAG-3 in dampening the immune response, high LAG-3 expression may be associated with decreased efficacy of PD-1 axis blockade. Additional studies to evaluate the predictive value of LAG-3 in patients with lung adenocarcinoma undergoing immune checkpoint blockade are warranted.