Triple-negative breast cancer (TNBC) represents a heterogeneous group of aggressive tumours which exhibit high rates of relapse and poor prognosis. There are currently no effective targeted TNBC treatments due to a lack of well-defined molecular targets. Recent innovative therapeutic approaches, including immune-checkpoint blockade, have taken to targeting the tumour-stroma in combination with chemotherapy. Despite successful advances in other solid cancers like melanoma, anti-stromal therapies have made little clinical progress in TNBC treatment. This has been largely impeded by a poor understanding of cancer-associated stromal cells (CASCs) and their functional heterogeneity underlying tumorigenesis.
To gain valuable insights into tumour-stromal biology in TNBC, we performed single-cell RNA sequencing (scRNA-Seq) using the Chromium Single Cell workflow (10X Genomics) on healthy and malignant breast tissue from murine allograft, patient derived xenograft (PDX) models and patients. Here, we predominantly focussed our analysis on the cancer-associated fibroblasts (CAFs), endothelial and perivascular cells, and identified conserved gene signatures across models. In particular, we observed intra-tumoural CAF heterogeneity and more particularly, we identified a cluster with functional enrichment for cytokine and chemokine signalling pathways, suggesting potential roles in immunosuppression and the recruitment of other CASCs to the tumour. We inferred differentiation using pseudotime trajectory analysis and identified the expression of key genes likely involved in the transition from normal fibroblasts to different CAF states.
Importantly, we observed similar populations of CASCs in primary tumours from patients with TNBC, highlighting key gene signatures of clinical relevance. This work demonstrates the power of single-cell technologies as a discovery platform to unravel the tumour-stromal ecosystem and identify novel anti-stromal therapeutic targets in TNBC.