NR2F1, a Tumor Dormancy Marker, Is Expressed Predominantly in Cancer-Associated Fibroblasts and Is Associated with Suppressed Breast Cancer Cell Proliferation

Simple Summary Tumor dormancy is a state in which some cancer cells are dormant by less cell proliferation, and are resistant to treatments, thus leading to late recurrence. As nuclear receptor subfamily 2 group F member 1 (NR2F1) is a biomarker of dormancy shown in experimental settings, we studied its clinical relevance by analyzing comprehensive gene expression profiles of approximately 7000 breast cancer patients using computational biological approaches. NR2F1 gene expression of bulk tumors correlated with the suppression of cell proliferation and metastasis-related pathways, but not with metastasis or survival. Using single-cell sequence cohorts, we found that NR2F1 was predominantly expressed in cancer-associated fibroblasts, particularly in inflammatory type, rather than in cancer cells. Further, NR2F1 expression in breast cancer cells did not consistently correlate with stem cell-like traits. Our findings suggest that the NR2F1 gene expression signal from a patient's bulk tumor is not from the cancer cells. Background: Tumor dormancy is a crucial mechanism responsible for the late recurrence of breast cancer. Thus, we investigated the clinical relevance of the expression of NR2F1, a known dormancy biomarker. Methods: A total of 6758 transcriptomes of bulk tumors from multiple breast cancer patient cohorts and two single-cell sequence cohorts were analyzed. Results: Breast cancer (BC) with high NR2F1 expression enriched TGF beta signaling, multiple metastases, and stem cell-related pathways. Cell proliferation-related gene sets were suppressed, and MKi67 expression was lower in high NR2F1 BC. In tumors with high Nottingham grade, NR2F1 expression was found to be lower. There was no consistent relationship between NR2F1 expression and metastasis or survival. Cancer mutation rates, immune responses, and immune cell infiltrations were lower in high NR2F1 tumors, whereas the infiltration of stromal cells including cancer-associated fibroblasts (CAFs) was higher. NR2F1 was predominantly expressed in CAFs, particularly inflammatory CAFs, rather than in cancer cells, consistently in the two single-cell sequence cohorts. Conclusions: NR2F1 expression in breast cancer is associated with tumor dormancy traits, and it is predominantly expressed in CAFs in the tumor microenvironment.