Baseline sLAG-3 levels in Caucasian and African-American breast cancer patients.

Background: Worse survival persists for African-Americans (AA) with breast cancer compared to other race/ethnic groups despite recent improvements for all. Unstudied in outcomes disparities to date is soluble LAG-3 (sLAG-3), cleaved from the LAG-3 immune checkpoint receptor which is a proposed target for deactivation in emerging immunotherapies due to its prominent immunosuppressive function in the tumoral microenvironment. A prior study has found that lower sLAG-3 baseline level was associated with poor outcomes.

Methods: In a cross-sectional study of 95 patients with primary breast cancer (n = 58 Caucasian, n = 37 AA), we measured sLAG-3 (ELISA pg/ml) in pre-treatment blood samples using the non-parametric Mann-Whitney u-Test for independent samples, and, calculated Pearson r correlation coefficients of sLAG-3 with circulating cytokines by race.

Results: Mean sLAG-3 level was lower in AA compared to Caucasian patients (1377.6 vs 3690.3, P = .002), and in patients with triple-negative breast cancer (TNBC) compared to those with non-TNBC malignancies (P = .02). When patients with TNBC tumors were excluded from analyses, the difference in sLAG-3 level between AA (n = 21) and Caucasian patients (n = 40) substantially remained (1937.4 vs 4182.4, P = .06). Among Caucasian patients, sLAG-3 was correlated with IL-6, IL-8 and IL-10 (r = .69, P < .001; r = .70, P < .001; and, r = .46, P = .01; respectively). For AA patients, sLAG-3 was correlated only with IL-6 (r = .37, P = .03).

Conclusions: We present the first report that African-American breast cancer patients might have comparatively low pre-treatment sLAG-3 levels, independent of TNBC status, along with reduced co-expression with circulating cytokines. The mechanistic and prognostic role of cleaved LAG-3, particularly in disparate outcomes, remains to be elucidated.