Our data of sustained USF2 protein expression during the secretory phase in eutopic endometria of women with endometriosis, an invasive estrogen-dependent disease, and the fact that the USF2 action is cell specific and may change its function from tumor suppressor to tumor promoter with invasive characteristics [15, 42], suggest that USF2 may be involved in the pathophysiology of the endometriosis. The gene discussed is USF2; the disease is endometriosis.