Previous studies have found that in mice, oestrogen exposure after ovariectomy significantly upregulated BDNF, but the hormonal fluctuations of the murine oestrous cycle did not [25]; evaluations of the plasma BDNF concentrations of endometriosis patients by ELISA showed that BDNF expression was not affected by the menstrual period [26]; other studies suggested that TrKB expression in eutopic endometrium has no correlation with the menstrual period [27]. This evidence concerns the gene NTRK2 and endometriosis.