With endocrine therapy (eg, tamoxifen, aromatase inhibitors), benefit depends on estrogen and progesterone receptor expression; benefit is Greatest when tumors have expressed estrogen and progesterone receptors Nearly as great when they have only estrogen receptors Minimal when they have only progesterone receptors Absent when they have neither receptor In patients with ER + tumors, particularly low-risk tumors, endocrine therapy may be used instead of chemotherapy.