In a canine mammary tumour study, OTR levels were higher in benign tumour tissues (6.42 ± 0.27, n = 19) than in malignant tumour tissues (5.75 ± 0.26, n = 24, P = 0.08), higher in malignant oestrogen receptor α (ERα)-positive tumour tissues (6.27 ± 0.21, n = 14) than in ERα-negative tumour tissues (5.54 ± 0.37, n = 10, P = 0.06), and significantly higher in histological grade I (6.2 ± 0.29, n = 10) and II (6 ± 0.53, n = 7) lesions than in grade III (4 ± 0, n = 3, P < 0.05) lesions [95]. This evidence concerns the gene ESR1 and breast cancer.