ESR1 and cancer: Examination of mRNA expression in all 21 cancer types revealed positive correlation between three NR gene clusters, namely 1) NR4A1, NR4A2, NR4A3 (NR class IV), 2) AR, ESR1, ESRRG, NR2E3, NR3C2, PGR, RORC, THRB (NR class I/II/III), and 3) HNF4A, HNF4G, NR0B2, NR1H3, NR1H4, NR1I2, NR5A2, PPARA, PPARG (NR class 0/I/II/V; Fig. 4A).