NR4A1 and neoplasm: Individually, both NR4A1 and NR4A2 exhibit pro-oncogenic activity in many solid tumors, whereas in many blood-derived cancers, NR4A1 and NR4A3 are classified as tumor suppressors based on the rapid development of acute myeloid leukemia observed in double knockout NR4A1−/−:NR4A3−/− mice [16,17].