Interestingly, in our present study, we observed high ratios of wt-ERα:ERαDel4, wt-ERα:ERαDel.7, and wt-ERα:ERαDel.3,4 in patients with endometriosis, which indicates that relatively more wt-ERα existed in endometriotic tissues and were thus exposed to more functional E2. Here, ESR1 is linked to endometriosis.