WNT/β–catenin pathway activation correlates with the increase of tumor-associated macrophages in triple negative breast cancer (TNBC).

Abstract

e12564 Background: Triple negative breast cancer (TNBC) occurs in about 20% of all breast carcinomas. Because only a fraction of TNBCs responding to immune checkpoint blockade show a pre-existing T cell-inflamed tumor microenvironment (TME), it is critical to understand the mechanisms of T-cell exclusion. Tumor-cell intrinsic activation of the WNT/β–catenin pathway, overexpressed in 30% of human breast cancers, is linked to a T-cell excluded TME. In β–cateninhigh TNBC, however, the quality of the myeloid compartment has not been evaluated. Methods: A total of seventy-five, early-stage, untreated, TNBC patients was assessed (patient cohorts approved by IRB). β–catenin expression was detected by IHC and scored as high, intermediate, and low. The presence of T cells, tumor-associated macrophages (TAMs) and LAMP-expressing dendritic cells (LAMP+ DCs) was assessed by IHC using aCD3, aCD68, aCD163, and aLAMP, respectively. Public TNBC datasets TCGA (N = 157) and METABRIC (N = 319) were interrogated for correlations between β–catenin- and immune-associated genes. Results: Three patient groups (N = 25/group) were identified according to the negative, medium and high intracellular expression of β–catenin. As opposed to β–cateninlow TNBC, the β–cateninhigh group displayed significantly lower CD3+ T cells (median 5% ±7.37 SD vs median 30% ± 18.28 SD, p < 0.0001) and LAMP+ DCs (median 1% ± 2.515 SD vs median 10% ± 7.038 SD, p < 0.0001). The β–cateninlow group was enriched in lymphocyte-predominant TNBC. For the first time, we show that the immune-suppressive, CD68+CD163+ TAMs were strongly accumulated in the β–cateninhigh group (median 20% ± 12.20 SD vs median 5% ± 6.831 SD, p < 0.0001). The interrogation of the public TNBC datasets TCGA and METABRIC confirmed that – after patient statification according to the expression level of a WNT/β–catenin gene-signature (i.e. MMP7, SFRP1, WNT10A, WNT16, WNT9B) – multiple TAM-associated genes – identified by our group in a single-cell RNAseq dataset – were strongly upregulated in WNT/β–cateninhigh signature, highlighting the role of the WNT/β–catenin signaling pathway not only in T-cell exclusion but also in selective TAM accumulation. Conclusions: Immune-suppressive TAMs are accumulated in β–cateninhigh, T-cell excluded TNBCs emphasizing the importance of tumor-intrinsic factors in shaping the quality of the immune infiltrate.