NR4A2 and non-small cell lung carcinoma: Of particular interest to us were the five nuclear hormone receptors involved in retinoic acid signaling: TR2 [14], TR4 [15], NURR1 [16], NOR1 [17], and the retinoic acid receptor alpha gene, RARA. Retinoids that activate retinoic acid receptor alpha have been shown to be safe and shown some efficacy in clinical trials with NSCLC [18].