At the physiological level, estrogen is not the cause of breast cancer.[28] However, either surgical oophorectomy or LH–RH analogs (such as goserelin, leuprorelin, and buserelin) can be used to treat breast cancer by reducing the level of circulating estrogen.[29,30] When breast cancer patients were grouped according to estrogen level, the recurrence free survival rate was significantly reduced in the groups with low estrogen level (10–49 fmol/mg protein) compared with high estrogen level (>50 fmol/mg protein). This evidence concerns the gene GNRH1 and breast cancer.