NR2F1 and neoplasm: Only a very small percentage (~3%) of primary tumor cells were positive for NR2F1 (Fig. 4b, “Primary Tumor” bar), consistent with data from head and neck squamous cell carcinoma (HNSCC) PDX models and human HNSCC tumors21 and the mouse mammary tumor virus-polyoma virus middle T antigen (MMTV-PyMT) model21.