NR4A1 and breast cancer: In agreement with previous studies, we found that triple negative, highly invasive and metastatic MDA-MB-231 breast cancer cells express high levels of Nodal and that hormone receptor positive, weakly invasive and non-metastatic MCF-7 breast cancer cells express low levels of Nodal (Fig. 5C) [10, 11, 13, 48, 49].