ESR1 and neoplasm: Interestingly, compared to the non-metastatic 67NR cells, the metastatic 66cl4 cells also expressed significantly elevated levels of Bmp4. Consistent with a role of these secreted proteins in metastasis, we found that high GREM1 expression correlated with reduced relapse-free survival (RFS) in estrogen receptor (ER)-negative breast cancer patients and that the association with poor prognosis remains, even with elevated co-expression of a BMP in the tumor.