A recent study profiling all NRs in ER-positive and ER-negative breast tumors revealed that while most NR mRNA levels were significantly lower in breast cancer versus normal tissue, the expression of all of the NR4A family members (Nur77, NURR1, and NOR1) were significantly up-regulated in ER-positive breast cancer (57). Here, NR4A1 is linked to breast carcinoma.