To assess the pattern of the expression of HO-1 in the endometriosis and OCCC, we employed archived biopsies from patients with clear cell EAOC (n = 17), endometrioma, a cystic endometriosis arising in the ovary (n = 5), endometriosis (n = 6) or control tissue from hernia sacs (n = 5). Here, HMOX1 is linked to endometriosis.